[Jlox1]

Help me understand whats the fascination with in ear anything, To me I have never found a pair that stay in my ear, sound as good as an over ear or don't have too much treble yet, why would anyone use them when they could just get some small over ears.. The only in-ear I have heard that I loveeeddddd were the bose IE2 like ever since I heard those my life has never been the same.. . 

 

[tinyman392]

In Ear monitors are smaller and more portable entirely.  This can also result in more potential chance that they'll be more comfortable.  Another huge plus is isolation that they provide without any active gizmos or batteries required.  You don't have to sacrifice quality either, for any given headphone in a given price range, you can find at least one IEM that has as good of quality.

 

[ori88]

I travel alot, and when doing so, portability and isolation are two key factors.  Over the ears don't block out enough of the engine noise or a crying toddler next to you.  This is very important when you need to wake up at 5am for a flight, work a full day, then fly back late at night.  
 
I used to have Shure E4c with the triple flange and they fit great.  I then switched to TF10s and the sound was dramatically better...but kept having seal issues.  I just got my TF10s custom molded and they're awesome.  No longer have seal issues, I can move my head around, yawn, etc... will try to hit the treadmill next.  
 
I have over the ears too, but I don't travel with them.

 

[Peyotero]

Stealthy in public. Can go to sleep wearing them. Very often are more detailed then full size cans. Isolation.

 

[DrGroove]

I find them far more comfortable, isolating, they don't give me headphone hair, easily driven.

 

[ori88]

Quote:

I find them far more comfortable, isolating, they don't give me headphone hair, easily driven.

headphone hair, good one!  forgot about that.

 

[NotSoSerious]

I think the biggest factor is the portability.
Iem's are the only type of headphones that actually fit in nice and snug in your pocket- you can take it well, just about anywhere, as long as you have a pocket. For full-sized headphones, or even foldable headphones, you'd probably have to carry around a bag, which isn't nearly as portable as a pocket.
 
Isolation is also a small factor. You can get better isolation with probably less money then headphones, while still having great sound.
Take the M9's for instance, they don't isolate that great, but they are definently a large step forward from the more expensive Ht-21's or the Portapro's.