[Alneyan]

Blood battle spells can still be used I think, when you have your back behind the wall and must deal as much damage as possible, since you are going to bite the dust before long; other than that, I wouldn't make the majority of them the cornerstone of any strategy. Blood has two spells increasing the strength of troops, and it's not particularly expensive as far as battle enchantments go, so you might wish to try using these spells (especially the demon variety, available very early). Blood also has a massive battle empowerment spell (+2 to all magic paths, if memory serves), but has the unfortunate tendency to bring in horrors, and only a Blood 4/Blood 5 mage will be comfortable using it. Still, if the horrors aren't too bad, it might work for a mage having a lot of random magic.

Other than that, Blood is a magic school you can usually get without a lot of work, unlike virtually every other magic school out here (Water being the other easy one to build from scratch). If you can get mages with a random pick in Blood, you can start up a very nice Blood economy at once, even with a low amount of blood hunters. Getting to level 2 will only cost you 30 slaves, and then you should try to reach level 3 by various means; once you are at level 3, you should have all your Blood needs covered. Besides, you can empower a mundane mage in Blood at a fairly low cost (50 slaves is easier to come by than 50 gems), allowing you to get all those summoning spells and to join in the fun.

In short, I would always try to build up a blood economy, unless playing Ashen Empire or something to that effect; lifedraining alone is good enough to warrant the expenses, and I would rather keep my Death gems (Wraith Swords, the other only option in town for lifedrain) for other purposes. Add to that all the other benefits of Blood, and you have a pretty strong case.