I find that a long-running Chrome instance will often start using huge amount of CPU time for no good reason (the Chrome task manager currently reports the "Browser" task is using 110% CPU and has used over 18hrs CPU time for my current instance). I've observed this on three different machines, one of which isn't used by me so there shouldn't be too much overlap in terms of sites used etc.
I almost always find that this is caused by a badly behaved website, not Chrome itself.
Some sites have horribly written JavaScript, or introduce ads that run their own CPU- and memory-intensive JavaScript.
Finding and closing those tabs, or disabling JavaScript, or using uBlock or uMatrix usually solves it for me.