so necrophos just got his Q mana reduced by 30 while it does not seems like a lot lets do some calculations
every last hit gives you 7 mana per second for 8 seconds so in total you get 56 mana per last hit
last patch you needed 190 mana so you need to last hit 190/56= 3.39 creeps to get you mana back
now you only need 160/56= 2.85 last hits to get you mana back .
that is 0.54 less last hits needed to sustain your mana , over the course of a game it adds up a lot
and the better part is that the level 10 talent increased the mana gain from 56 to 70 per last hit
so with old patch manacost and level 10 talent you need 190/70= 2.7 last hits
and with new patch and mana cost you need 160/56 = 2.85 last hits , so we allmost got the level 10 talent for free in terms of mana sustain as long as we just use Q
sorry for bad english
Source: https://www.reddit.com/r/DotA2/comments/11nsos7/necrophos_buff_migth_be_more_substancial_than_it/