All IGH need a way to tension the chain (or band). This can make a difference to the ease of use (wheel change etc).
The simplest way is horizontal dropouts.
The crude way is a spring-loaded chain tensioner on a conventional vertical dropout.
The slick way is sliding vertical dropouts.
The creaky way is eccentric bottom bracket (EBB).
My bike has EBB, it is not really so creaky as its rep but there are several ways to keep the rotating eccentric in place:
-external clamps
-set screw
-internal wedge
-internal wedge with a release.
I prefer the external clamp or the internal wedge with a release. The set screw can be hard to make fine adjustments and the plain internal wedge can corrode into place.
You can get external EEB units that fit onto normal bottom brackets.
Phil Woods does an eccentric block for BB30 press-fit bearings, which saves a lot of weight.

If you run disc brakes you need to maintain the pad alignment during tensioning, which doesn't happen with horizontal dropouts.