- Being able to see effectively installed modules. Sometimes a module is unexpectedly installed (or not) and you want to be sure. If it's listed in this screen, you know it's installed.
- Being able to disable the frontend rendering of a module without turning off its code. This is useful when a module is a tight dependency or when you just temporarily want to shut something up. ;) I think it would be clearer if this feature were named something different, but naming things is a hard problem.
- Being able to enumerate all the modules. This differs from #1 in that it lets you get a general idea of the modules on a particular system (for example a production system) without needing shell access or taking any risky actions. (That said, being able to view installed modules shouldn't necessarily be the same permission as being able to disable their output.)
I know Magento 2 is working hard to strip out unnecessary tight dependencies between modules in core,