Santa Muerte's Viral Marketing
Santa Muerte, the patron saint of love and lost objects, lets me in on a her secret why traditional magic so often requires sacrifice- and altars.

In traditional Western magical tradition, it is very, very common to make some kind of deal with an external entity, who will then grant you some kind of power, but usually command a very steep price.
For example, traditional folk magic from Germany has it that you can marry a nymph. First you need to find a nymph, and call out to her, and then you woo her, and when she feels ready you take her down to the forest with actual witnesses and have a wedding ritual, and then you wear the ring, and you don't marry anyone else, and you most certainly don't commit adultery by starting anything informal with a human woman. If you do all these things, of course the nymph will help you with all that is in her power, as any loving life partner would, which in her case means to adjust coincidences so that you achieve great success and fortune. Of course, the stories go, eventually the sacred vows are usually broken and great tragedy comes about. Look out for rich old (apparent) bachelors to find people who stuck to the deal.
Now, if you are actually genuinely and intrinsically interested in marrying a nymph, or any other nonphysical being, by all means go for it- I am not here to judge how people are to find happiness. Of course, if you are interested in having children, you will get the same relationship issues that you would get with anyone else with a different view or ability on the subject. And, if you rely on the marriage to the nymph for the wealth, you may well get the same kind of conundrum as you would relying on your marriage for wealth with a physical person. It is just that cheating on a nymph is even worse than cheating on a physical woman, because she immediately knows it, and you can expect to immediately experience her wrath.
I have had very pleasant conversations with nymphs, but I would suggest to keep it within the bounds of friendship unless you are quite serious about what you are doing.
So apart from being rather male centric, this wonderful (for a magic historian) 17th century nymph spell exemplifies wonderfully the trouble with Western magical traditions (at least all I came by so far). It's always some variant of the impossible bargain. Of course the darkest kind is the one with the devil, or some other kind of evil entity, where you hurt someone in order to get the favor. It would appear that that kind of deal was not particularly rare among aristocrats in recent European history looking to move up.
Now, as a Huna practitioner, I don't do deals that require payment. The sixths principle says that all power comes from within, so what I do with my power is mine, and that's that. I'm not saying entity deals don't work- but I am saying that they work because they are a means for tricking yourself into believing in yourself and achieving things with your own power. The nymph spell above was found among the personal items of a 17th century wagon smith who somehow came to wealth as a trader. That is not a particularly normal situation for the time- so it must have worked for him! Maybe he even managed to trick himself somehow into making provisions that would allow him to marry after all, but I don't envy the wife so much, with the nymph always hanging over her head. If enough emotion's involved to change his reality, personally I'd consider it a metaphysical affair and would want it to stop. Of course he could do that- but then he would have to find additional ways to keep up the believing in himself, and to part company with the nymph in a friendly way.
I'm not even saying that entity deals are never worth their price. If it's the easiest way to get yourself to believe you can achieve something, and the price is acceptable, and the entity is genuinely well-meaning and friendly, by all means go for it. Just be wary of long term commitments, they look a lot cheaper when you are making them than when you are fulfilling them- it's essentially the same problem as with loan sharks and cell phone contracts that come with an iPhone. Also, make sure that you know how prices will grow when your wishes grow- Even if it only takes a drop of blood to power a love spell, I still would much rather not poke myself every time I'm in need of a little affection. And what if I want more? By the logic of the drop of blood, I would likely have to up the ante proportionately, so for the biggest favors, I would have to make the biggest sacrifices. You can see that this is not a direction you want to end up going in if you think it through. Here's an alternative.
If you can get yourself to believe in your own power, you're free! And free is a lot cheaper than cheap. When a change in energy is large enough, it changes quality. When you don't have to worry how many rosaries you need to say to get a new lawnmower, you are free to ask for a waterfront property.
The downside is I don't get to use any shortcuts, I need to get myself to believe that I have power on my own. I usually use imaginary experiences to accomplish that, and also accepting the friendly Huna philosophy that says that beliefs are arbitrary and I can pick any I like make them mine, and also that I already have my own higher aspect that powers everything- I am my experience. The combination does the trick fairly well. But it does take effort, and it does take practice- but hey, so do the bargains! So the limiting factor is no longer what some entity demands- it is simply the practical issue of how many contrary limiting beliefs you are willing to dig up and turn around, and how much more energy flow you can tolerate going through you how quickly, because suddenly getting stronger energy flow really can be like a wasp's nest for your fears.