For me, nothing beats the small size and convenience of IEMs. My RHA 750 and Shure 535 sound great. Thinking about some customs....
The often overlooked disadvantage, to me, is that if you're interrupted and have to remove one of them to hear someone, it takes a few seconds to replace them in the ear afterwards. As opposed to on-ear or over-ear headphones that are easily placed over the ears.
Also, people don't always notice the IEMs and will speak without realizing you can't hear them. With headphones, they will wait until you remove them.
The often overlooked disadvantage, to me, is that if you're interrupted and have to remove one of them to hear someone, it takes a few seconds to replace them in the ear afterwards. As opposed to on-ear or over-ear headphones that are easily placed over the ears.
Also, people don't always notice the IEMs and will speak without realizing you can't hear them. With headphones, they will wait until you remove them.