Rest-pause is an old-school bodybuilding technique of performing a set to failure, resting a few seconds, then squeezing out more reps. The idea is simply to get a little more work in even after the muscles have been exhausted.

Is it OK to pause workout?

Unless you have a coach that wants you to use the Pause button a certain way, it's up to you if you should pause or not. Plus, you don't need to decide if you're one way or the other. It's perfectly fine to use pausing on occasion, but you don't have to use it every time.

Is it bad to pause during a set?

Instead of making the last rep of each set a paused rep, however, you do paused reps for the last set of one or more compound exercises in your workout routine. This is a particularly good way to stress-test your form, as any flaws will be magnified by the fatigue you feel after doing several regular sets.