My eyes have been opened O_O

Math ftw

Actually its your total health and mana regen... so it stacks last..... If you built items with mp5 or hp 5... it increases that.... Its way better than a slightly less re-spawn... Don't look at its benefits from base... look at it when you have your items... Perseverence is totally the best pick.

Even though the difference is minute, it's probably more often the case that the tiny mana regen letting you cast one more skill made a difference than respawning a few seconds early to try and save an inhib when the rest of your team is still dead.

end game you'll probably have a max of 50hp/5 secs (starks/randuins is ~+30hp/5)
with 4%, it becomes 52hp/5secs
so that's an additional 2 hp every 5 secs when you have 2k hp
that's 1/4 of a rejuv bead, imo not worth it

early game you probably have a max of 15hp or mp/5 secs (doran's shield is +8hp/5)
with 4%, it becomes 15.6/5
so 0.6 per 5 secs
say you stay in lane and don't recall for 10 whole mins, that's +72hp/mp

Two words: Blue buff.

If you get blue buff. Perseverance gives you some extra mana regen almost equivalent to the mana regen mastery 2 rows down.

Ive actually change mastery builds because of this
Mind you, its changed my utility build more

For those arguing in favor of the blue buff for perserverance, i'll be honest with you, if you have the blue buff there is pretty much no reason you should be completely oom to the point where the regen is actually worthwhile, if you are then chances are you are being wasteful with your mana, i used to use perserverance until I actually thought about the ddifferences, stop jumping on the forum-express where 1 person's incorrect opinion becomes held as fact(IE perserverance is actually better or berserker greaves are never worth it, etc)