Here's a few reasons for them. They're a little more fun than not using them, why not make having a cup of whatever a fun event instead of just having a drink? The mugrug won't break if you drop it. It will soak up spills too. I wash dishes by hand. A mugrug can be tossed in the wash when it needs it.
If you want to make them, go ahead and make them and have fun doing it.
Rodney