Now with solo kata, and kihon aside. I don't think any karate techniques should be practices in thin air. You should always be hitting or lifting/moving something. Makiwara or kigu undo are super import at for this. The conditioning and to int is a nice side effect but the main thing to focus on is how it teaches you to connect your limbs to your body and your body to the floor, you can't achieve this in Thin air.
If your not hitting a pad or makiwara, or using kigu undo tools, then hopefully you have a partner to hit/move/throw/grab etc. you have to develop feeling.