@froggyfan1 Depends on your without frequency. Workout body part once a week you can go to failure. Work out twice+ per week.. get close to failure but with 1 or 2 more left in the tank.
Big muscle and small muscle.... Small muscle can go closer to failure as it can typically recover faster.
@froggyfan1 It depends, on the big compounds (squat, bench, deadlift, OHP) I like to go about 1 or 2 reps shy of failure.
Isolation movements (curls, leg extensions etc.) are another story, I find you can go to failure and in some cases even beyond failure (forced partials) with great success (though tracking might be more difficult). This is all individual though, but as long as you can progress I’d say go all in on your isolations especially if it’s the last set of a given exercise.
@froggyfan1 You should be doing every set to or very close to failure (0-2 RIR). If you've been leaving reps currently then I recommend doing 2 sets both to 0 RIR and you'll probably end up with more stimulus from less fatigue.
@froggyfan1 I like to build up to my max effort set(failure), do 1-2 set, drop down to 80% of top set weight and do another backoff set. Depends a lot on the exercise though and also how early in the workout given exercise lies.
Straight sets are usually my go to as I reach the half point of my session.
And sometimes finish off a muscle group by using an intensifier.
@froggyfan1 There is no right answer to this without context.
If this is the first exercise of a workout using an upper / lower split, then I'd say none of the sets to failure, if it's the last exercise for that muscle, I'd say either option 1 or 3 are solid.
If it's part of a full-body workout you do 3 times per week, you might even start with 1 set per exercise (close) to failure and see how you progress and recover, then once you stall, try to add a set more, keep the first a bit from failure and go for failure on the second. When you stall on 2 sets, repeat the same procedure with the 3 sets. When you stall that, consider changing the split or programming, eg to a higher RIR, or programmed rep / intensity changes, etc.