A training partner can be either beneficial or detrimental to your workouts, depending on your type of training, routine and who exactly you choose to be your partner. Obviously someone who isn’t as committed or serious as you will likely stand around, chat, hold you up and be a hindrance to your routine.
However a good training partner can be priceless with motivation, spotting your last reps when needed, and pushing through barriers. It’s good to have a variety of training routines you can do both with and without a partner as both have pro’s and con’s. The only thing to think about is to choose your partner wisely, someone who more advanced than you will often be much better to train with than someone at your level.
Training with someone more advanced than you will usually push you more and you will be determined to lift the weights they are, and to look like they do.