It actually give effectiveness(base unaltered effectiveness is %70 (0.7), gets multiplied by nearly half of the skills, defence, attack, but not all ofc) up to +%25 percent (you get another +5 for every level, so effectiveness may go up to %120 since max level is 5) which makes you really stronger overall.
I wanted to add what attribute does what as tooltips, but I kinda got exhausted :D and I lightened my conscince by thinking, they already see stats roughly, if they wanna see what int does they may increase it one by one and see what changes lol (sry I got to be a bit of an unresponsible slouch as I got tired :3)
Need 2-2-2-2 base stat guys to obliterate other max level guys btw, unless you are really unlucky :D
Thank you for playing!