Especially useful for 3D. For a more realistic 3D, a high refresh rate is required, of course, if your gpu is support that , you'll play more smoothly.
But in the normal image, however, there is a remarkable difference for professional players. It is possible to understand this when playing games with high FPS.
It is generally recommended for competitive games. For example, if you play games like cs: go, racing and lol, the difference is clear.
I think 144 hertz monitors can be taken if budget is available. If not, you don't have to. It is also difficult for return back from 144hz monitor for accustomed users.
Yes, but usually it's useful for FPS(First person shooter) games.
Normal users probably won't be able to notice the differences between 60Hz and 144Hz.
If you decide to buy a monitor with 144Hz, you need to buy a powerful GPU too, because with a weak GPU, you won't be able to use 144Hz capability on your monitor. Powerful GPU = need a decent(or quite strong) processor too, so it won't have bottleneck.