If you think of training as an empty cup, and you think of the method(s) you plan on using to fill that cup with, eventually too much of anything one thing, especially done for too long, will just spill over and become useless. This happens when either something has already done its job, or is taking more than it can give back.
Volume for the sake of it is pointless. Do enough work to stimulate strength/growth and then give the body room to breathe so it can benefit for it. When all of those extra sets and reps simply eat into recovery and cause a deeper fatigue curve, then volume is taking away more than it can give.
Training past failure (forced reps, then forced negatives) is incredibly hard on recovery, and honestly, there's no point in it. Again, a case of taking more than it gives back.
Remember that your support work should do a few things....
1. Improve the main lift
2. Keep you injury free
3. Build muscle mass
That's pretty much the whole ball of wax.
Believe it or not, you can usually the eyeball test on a lot of guys to determine what they need to do. In every single case? Of course not, there's always going to be an anomaly.
However technique aside, it's not hard to figure out if a guy can't squat for shit and has shit quad development to go with it, that he may need to get on that.
If a dude can't bench and his arms and shoulders suck, well he should focus on building those areas up.
If a guy can't pull for shit and his upperback isn't well developed then he'll need to build a strong and massive back.
These are not hard concepts obviously but they are missed by some because they are constantly trying to figure out the lifts, which they should be. But then they lose sight of the fact that the actual muscles do in fact, do the lifting.
So guys should be focused on increasing muscle mass, obviously, and so of course that means filling out their frame with movements that help the big lifts. These things go hand in hand.
However what I see a lot of, are guys not always understanding when a lift or movement has outlived its usefulness, or isn't the dragon you should be chasing any longer.
If your main lift starts improving shortly after the addition of a new movement to support it, then progress on that assistance movement and keep it in so long as the primary movement is improving as well.
So if you add in dips, and progress from 75x10 to 100x10 pounds on dips, and your bench started improving as well, keep the dips in so long as you're seeing progress on the bench. It's possible the dips improved something muscularly that was lacking in the bench. However once that area is strengthened, there will come a point where dips outlive their usefulness, and you may need to focus on something else. Getting stronger at overheads, or incline, etc.
Rows are a great example of this. I've been busting hump on barbell rows for a little while now, and I definitely feel it is helping my pull. However once I can do semi strict rows with 405 for 6,8,10 whatever....I have a pretty good guess that trying to move up to 425, or 455 is just going to turn into a shit show of a movement and probably not benefit my pull at all. I could be wrong, it's just a guess. However 405 pound strict barbell rows is pretty strong. So I don't feel like I'll need to get much heavier than that. I would simply need to be able to move it with more control.
It's the same with good mornings. I found a long time ago that doing good mornings with 185-225 pounds was far more productive than doing them with 455 for reps. With the lighter weight, I could get deeper in ROM, and really FEEL what they were supposed to be doing. Anyone that's doing good mornings with more than they can squat, aren't doing good mornings. They are doing something else, or they suffer from some serious quad deficiency syndrome. But even in this case, there will be a point where I'd either have to move up heavier in good mornings, do more work, or change something in order to milk more out of that movement. Eventually, doing them will simply serve as maintenance work for good mornings. There won't be any more carryover or usefulness in terms of what it is providing.
The 100 rep curls are another great example of this. I used those to help with elbow pain, and create some bicep growth. Eventually working up to 200 reps on them. However I found that simply staying with a set of 100 just a couple of times a week did the job, and worrying about progressing on these didn't seem to offer a lot in the way of extra benefits.
It's up to you to be cognizant of this with the movements you pick to help get you better. It's another great reason why I don't do a lot of different things at one time. You can't always tell what's helping your ailment if you're taking a thousand medications.
Pick a movement to help your main movement to help the main movement, and progress on it and milk it as long as you can (and as long as it's helping the main movement). The main thing to have in mind about it is, know what strong is, in relation to it. So if you can do lunges with 315x10, well, you don't have a quad or glute weakness. If you can overhead press 315 for reps, it's possible your shoulders are already strong. If you can do rows with 400 for reps without monkey fucking the bar, that's pretty solid. Understand you can overrun the usefulness of a movement, that way you can drop it and work on finding something more productive to implement.
Everyone have a kick ass Friday, and epic weekend.