You're right - you don't need one. But there's also no specific harm in having one.You don't need training partner to train pre-defined drills. You can train solo and still get the same benefit such as
- jab, cross combo,
- roundhouse kick, side kick combo,
- side kick, spin back fist combo,
- ...
The benefit of partner training is your opponent can
- escape your attack so you can take advantage on his stepping back (train your chasing footwork).
- block your attack so you can take advantage on his blocking (train your grab, arm wrap, pull, ...).
For example, if your opponent blocks your punch, you can grab his blocking arm, pull his arm, you then punch with your other hand. If your opponent just freezes and doesn't evet block your punch, how can you practice your grab, pull, and ...?