These are my thoughts on if incorporating failure is the only way you can get good gains in the gym…
Lets get things straight first, if you are using training to failure to maximise hypertrophy (muscle gain) in your gym sessions without following a well designed periodised training programme then you are selling yourself short. I see far to many gym goers incorporating training to failure into their random routines without even considering progressive tension overload. If you are training to failure every Sunday without following a structured training programme then all I can suggest is PLEASE STOP!
There are times when I would avoid training to failure, one of these is If you are a beginner. I would avoid failure until you have technically mastered an exercise; this is when you can even start to consider training to failure on that given exercise. This could take anything up to 6 months. Piss poor form + failure = injury. I would also advise avoiding failure on some of the big compound lifts such as back squats, deadlifts & bent over rows as there is a higher risk of injury due to fatigue setting in. I would use sparingly on exercises like bench press (definitely use a spotter) and pull/chin up variations. Exercises that isolate muscle groups are probably best for incorporating failure.
I would recommend limiting training to failure to 20-25% of working sets on any particular muscle group (could go up to 50% if an advanced gym goer). An example of this is if you are doing 8 total sets for chest split into 2 exercises then i would have one set from each exercise taken to failure (usually the last set of given exercise)
So overall, failure isn’t necessary to achieve hypertrophy as long as you are achieving progressive tension overload over a period of time. Its an option you can use if you choose to and can help bust through them long standing plateaus if used wisely. Its another tool in the toolbox.