It takes skill and experience to know when to push out reps without overtraining and injury. Strength coach, Adam Bornstein recommends before you decide to lift to failure you should ask the following question:

What is the amount of skill the exercise requires?

The more skill required for a lift, the less frequently it should be performed to failure. Conversely, the less skill required to perform a lift the more acceptable it becomes to train to failure.

Snatches, for example, are arguably the single-most complex lift and lifting to failure is dangerous. Simpler multi-joint movements, such as variations of the chin-up, bench press, and lunge, are suitable for failure-based training but should be performed with extreme caution. Same can be said for exercises like squats.

Finally, single-joint exercises, including bicep curls, triceps extensions, and calf raises, are the least complex of movements and are far more appropriate exercises to push for the one last rep.

Now you can make informed choices and avoid overtraining and injury when lifting to failure.