Apparently the system process imagent is broken in Mac OS Sierra.
It consumes more memory than it should making your computer incredibly SLOW (up to 4GB and it keeps going unless you stop it).
In Mac OS Mojave it consumes up to 30MB which is alright.
This script will watch and kill the process if it reaches the specified threshold (60MB by default)
The easiest solution would be upgrading to the latest OS. However I know that some people can't do this because some stuff is still not supported in Mojave. So if you are one of us I hope this helps you 👍