From my own experience, as i literally play with anyone & any skill lv.
1. I play with my close friend (kinda my best match partner).
This one when im seeing some good unknown player from other court & im kinda ithcy to challange them. I will go out with my own best match agains them.
2. I play with different skilled player randomly.
This where i learn to adapt with different player style & habbit while also work on your strategy. Learn to observe & trying different strategy to win agains the opponent. Coz its mixed skill games. It wont be a fast pace all the time, so its easier for learning unlike when you play agains the good one, you wont have enough time to think if you are not used to it especially if you are under preasure. & last as its mixed, you learn to experience all different situation.
3. Play with lower level.
This where i did more mischieve

. Coz they are beginner, its not quite punishing when you do mistake, so trying new trick would be fun with them.
Also i can train my bad technique with them & bad return wont be much dangerous. Like for my case drop shot & net shot. The result are my bad shot become better & less likely my opponent able to take advantage over my weakness.
Thats from me, hope that help but if you are casual player with no coach, i think it better to find friend with similar level to play with. You train together, try to beat each other, & teaming up together when needed to have best match partner. Coz alone, your limit are just the club level you join in. When you had become the best in the club & you will stop growing for sure.
Also, if this is your first time taking lessons as well, and I mean no offense by this, you might find that you need to relearn basically everything from the very beginning. So you and your friend may end up starting from the same or similar place anyway.
Sent from my SM-G965W using Tapatalk
and i also agree with this one. Especially when your friend are totally new. Even if you are as good as you claim, as you train together, you will have to start the basic with your friend. You cant ask advance training while your partner cant even do the basic thing.