I finally found a negative in IEMs that I find pretty annoying.
If you get an ear infection in one ear, it feels like you have channel imbalance going on with the pressure feeling different in each ear.
I imagine headphones wouldn't have that problem, since they are out of your ear cannals.
Here's another one, what if the IEM was the cause of the ear infection or made it worse?
P.S. if you really have an ear infection, that sucks and I hope you feel better soon. I haven't had one in ages but they can be pretty terrible.
Ear infections never become really major problems for me (never really had a major one though). I got scared and thought I broke my IEMs. But besides that, nothing too bad.