Mages gain passive benefits of their path levels I believe.
+1 defense per lvl of water
E - +1 Prot
N - unsure
B - +1 str?
D - unusure
A - +1 precision
F - +1 attack
S - unsure
AFAIK
Edit (there's probably already a list out there somewhere though)
F - +1 Atk/lvl
A - +1 prec/lvl
W - +1 Def/lvl
E - +1 prot/lvl
S - Unknown
N - Increases max age, +10 supply/lvl, increased regen affect from cast spells (mechanics?)
D - Boosts fear (mechanics?), reduces old age afflications (mechanics?)
B - Assists in blood hunting (mechanics?)
Death reduces your chance of getting old age afflictions and boosts fear if you have it/gives you fear when you get enough death magic.
I think blood just helps with blood hunting.
Nature increases max age(or is it reduces your age..) and boosts how much regeneration you can get from spells you cast.
I don't know if astral does anything but it offers mind hunt protection.