I made an observation with a beginner band that shares our band room. We had rehearsal scheduled and they played just before us, I arrived a bit early and they let me sit in the room and listen.
Everyone was playing the same song in the same speed, but also, everyone was in their own bubble. Some of them because they were beginners and needed all their concentration getting through the song without messing up and some of them because they have overinflated egos and think the world, and therefore the band, revolves around them.
This created slight gaps, and a drifting feeling. It took me a while to realize what's wrong. No one in the room listened to the song. Everyone only had ears for their own instrument.
This is an important thing to learn as early as possible.
A beginner can be totally stressed for the fear of ruining the song for everyone else, and therefore play extra tight, with a laser focus on their own playing. By this, they will ruin the song - with good intentions. It's important to listen to the song, to what's going on in the room.
With an in ear mix, you can of course set everything nice and tight, and then boost yourself by 9dB, so you have a perfect impression of all the finer nuances of your playing, but it's actually impossible to listen to the song.
I did, for a while, experiment with that and changed my preferences. I usually started with a nice mix where everything is present, then raise the kick and snare by 3dB and the bass by 6dB, so I had a mix that made me play in perfect sync with the drummer, listen to my bass tone and still have the band mix present. Nowadays, I have my in ears set to a nice, balanced mix. The way I'd mix it for the audience, would I do FOH.
Less me, more band. I'm grooving much better this way.