How you do your reps in your exercise move is far more important than how many reps you do. Your exercise should be of quality, not quantity. Because it must be all about quality, each movement of the exercise will be focused and performed with purpose and diligence. It is common practice to go for the number of repetitions. If you alter that practice and opt for some other factor (such as time), then you will focus on quality. For example, you could try doing 35 seconds of lunges instead of 10-12 reps of lunges. Later, after mastering your form, you can perform lunges reps.
Also, you can overextend yourself in certain exercises. From my personal experience, I have tried to maximize pull-ups. I ended up overextending my shoulder joints. This affected my overall upper body routine. I should have initially focused on mastering my pull-ups. 2-3 reps of a good chin-up form is more beneficial (and safe) than 10-12 awkward forced reps of chin-ups. By keeping my abdominal muscles tight, keeping my shoulder joint tight and secured, and maintaining my proper form (perhaps testing them out using a chair or bench), this would have prevented injuries that could have a prolonged effect on your exercise routine. As I discovered, your shoulders are a delicate and intricate joint. It requires you to have mobility movements (for example, shoulder rotations) and static stretches (for example, shoulder pulls or hanging from a chin-up bar) with strength exercises (for example, vertical rows and chin-ups).
This is the lesson of quality, not quantity.
Another example of quality over quantity concerns performance. I love running. It is one of the best exercises to speed up the metabolism. Now, most people would assume that the more you run the better. They would jog, walk, or run for hours like a marathon runner. Instead, for your general fitness, interval runs and sprints are better (and shorter). This would be great for your joints and your overall fitness. Both a marathon runner and sprinters are excellent athletes. But I’d rather look like a sprinter than a marathon runner. It’s about quality over quantity.
A final example would be push-ups. I thought and assumed that the more push-ups the better. Once you have mastered the push-up movement, you should perform more complex and compound push-up movements. It is important to master the push-up movement first. You must keep your abdominal muscles tense. You should be able to keep your body (eg your back) straight during the movement. Later, you can do palm push-ups, plyometric push-ups, T-push-ups (or yoga), etc. to challenge and give more quality.