We all know the feeling of skillshots like 
missing by a full 
only to register a hit anyways because the indicator outright lied to you.
Yes, over the years, I have learned the actual hitbox sizes of many skillshots, but champions have different sized hitboxes as well. Besides, for the sake of new players, indicators shouldn't be outright deceptive.
Also needs a few of them indicators.
Don't forget the error from terrain height.
It isn't that much related to hitbox clarity:
Riot did confirm a while ago (On a old "Ask Riot" or a community gameplay post back when Riot cared a little more about its community) that some projectile hitboxes (mostly line grabs or hard CCs) do have, on top of having a line shaped hitbox, an extra "hitscan" zone, shaped like a circle at the extremity of the skillshots, which result in hitting things they never ever touched in the normal hitbox simply because that questionnable hitscan circle overlapped their hitbox a little.
