Making T-shirts (and other knit fabric clothing) with a serger is so quick and easy. A lot of people make pillowcases and pajama pants. The hem on knits isn't done with a serger. It usually looks best with a coverstitch machine, but can be copied wit a double needle in a regular sewing machine. I know some people make quilts with them, but not detailed, pieced quilts.
It's also handy for finishing the raw edge of fabric before you wash it, so it won't unravel.
I keep my serger up and ready to use, and probably use it every month.
I just made 10 chair covers from knit fabric, on my serger, to cover the ones at work that are showing their stuffing.