What possible use is Blood Magic?

I can't fathom how this could ever be a good idea. Maybe my lack of imagination, but I cannot see a situation where I would ever want to be spending life over mana to do stuff. I'm sure there's some combination I haven't thought of, but damn it sounds like a terrible idea.

Gems with lots of supports can be pretty hard to maintain with mana, unless you invest into a bunch of mana/mana regen. With good life/life regen, you can just cast off your life and not make a dent, and don't have to worry about spending those precious skill points on mana nodes.

Also, if using the Blood Magic support gem on your skills, you can reserve all your mana with auras.

It's not a bad idea when you can have a high hp pool with high hp regen. This in conjunction with the FACT that the life leech gem gives more % return than a mana leech gem can. The other reason blood magic is good (for some builds) is that you can use a bit of your hp to use some extra auras. With my current build I can rely on my hp for skills (my hp never goes down despite using it for my primary skill), and I can use the mana (that would otherwise be used for skills) for auras. Ah, and if you do get a 6L weapon, the mana cost is insane (depending on what supports you combine your skill with). BTW, I am also a crit build, so when I do crit (which is like 90% of the time), I heal back my life quickly... even though I am using blood magic with my primary.

if you're duelist or marauder you'll gimp yourself trying to get by on mana.

the amount of life you use for your skills is petty compared to damage taken, and it's very easy to leech/regen life when compared to mana.

I went straight for it as quick as I could on my duelist.

For many tank builds you'll want to spend mana on auras and spend life on active skills.

I hate playing without blood magic lol, I usally spec life nodes and damage, no mana and mana regen, so even spamming LA/FA/WED/Chain/Life leech something like that takes 66 life, but with life leech without hitting something impossible to lose health

but as a melee or bow user when I take no mana nodes blood magic is the way to go and using auras like anger wrath grace only cost 200-300 life with reduce mana at all lvl 20. So when ur over 3-4k health you don't really see losing any health

200 hp regen says hi

Why would anyone wanna use mana? Goes oom alot unless horrid mana nods/item stats are invested in.

So from what I can tell from most of these comments, blood magic is good for skills and mana is good for reserving auras. Then what is the point of the Blood Magic passive?

BM is great for someone who stacks auras. They can use their main dps skill with the BM support.