Mini washing machines are a convenient way to lengthen the amount of time between laundromat visits when you live in an apartment or dormitory. Admittedly, you're not going to use them to do all of your laundry, but they can really help out in a few ways:
Small Personal Items
Items such as socks and underwear can build up quickly. Often you have plenty of everything else, but are on the last clean pair. Rather than making a trip to the laundromat sooner than expected, you can easily wash them at home.
Delicates
For those items of clothing that are delicate and light weight and require a gentle wash, mini washing machines are perfect. You can wash and then hang dry without having to hand wash or go to the laundromat just for the delicates. You don't have to worry about the big industrial machines of the laundromat tearing them up either.
Unexpected Stain
Just went to the laundromat last weekend, but you've got a nasty spill on your favorite blouse? Don't wait until your next trip, you can wash it as soon as you get home. This minimizes the time that the stain will set, thus saving it from being ruined.
Camping
They're also great when out camping. By the end of a camping trip, you usually welcome the feeling of clean clothing and the last thing you want to do when you get home is a mountain of laundry. Take care of the smaller stuff before you get home. This way most of the things that you need to wash are bigger and are less tedious to fold and put away. Mini washing machines are compact in size and should easily fit with the rest of your gear.