Depends on how many sets/ intensity/etc.
Nothing wrong with going till failure - as long as you allow enough recovery time for your CNS before going till failure again. If you're going till failure and doing more than, say, 15-20 reps then you're sort of at the limits of usefulness. If for instance you're doing like 15 sets of 20 reps and by the end of the workout you can't even lift your arm up with no weight what-so-ever then you're a sadist with a lot of time to waste.