I'm not an expert but will do my best to explain.
Gsync/Freesync is basically a technology that allows more frames to be consumed by your monitor than your monitor can handle without tearing (a bit like VSync does). i.e. if you card can run a game at 200fps but your monitor is only 60hz then you will get massive screen tearing unless you cap the card to only do 60fps which is a waste if your card can do more. Running that same screen at 200fps in that example will look terrible. Gsync/Freesync still limits the frame rate but does it in a more elegant way than Vsync used to. Refresh rates were always amazing on TN panels but they look washed out and are terrible from an angle. IPS has always looked the best panel wise but suffers from it's own issues of glow and bleed, until recently it couldn't refresh fast enough for some games (like FPS) so it lagged. LG and others are finding ways to solve that though. VA and cheaper IPS suffer from terrible ghosting.