Doesn't make sense, why not report a clear troll if it doesn't cost you more than the 2 seconds it takes to click a button?
Isn't there a chance they'll end up in your next team or even worse piss off someone else enough to continue the vicious cycle of pettiness?
Break the cycle, see a troll report a troll.
Thank you for your time.
P.s. Just had a game where most of us agreed to an open game due to a 1/10 full crit Ryze top lane only to change our mind and drag it out as long as possible when the enemy team antagonizes the situation by saying they WON'T report him after game............... Probably created 4 more trolls for the next game.