Placing Handling Mod's is particularly good upon your TearBlast and Precision Arrows Bow because it lenghtens it's accuracy loading time a lot allowing you to fire it faster too.

Slap them on a ropecaster and you can tie down anything in seconds.

Thought it helped with aiming bow? was pretty sure it helped with accuracy. Seemed without it my arrows were way off course even when charged. With around a 100 handling still seem to not have total accuracy but can atleast hit the general area.

Googled it ->

In simple terms, handling is primarily best described as the rate of fire and reload time. This is because the game does not completely have conventional guns and heavy weapons; its arsenal consists largely of bows and arrows. This is thanks to the game's setting in a very post-apocalyptic world.

all of the weapon stats and what they do are on the Weapons inventory tab on the right side

Handling improves a couple of things:

Primarily it improves accuracy which means your ammo has a better chance of actually hitting what you are aiming at, especially over distance. You'll really notice this when aiming at either small objects or specific parts of machines. Ever aimed at a Watcher "eye" only to see your arrow fly past hitting nothing but air? Increasing Handling will allow you to hit more often and therefore miss less often.

Secondly it improves your reload speed which means you'll be able to reload ammo faster, which then allows you to fire more often.