I have lived my entire life without having one. This apt comes with one and it needs to be run at least once a month, otherwise dire things happen to the plumbing.
So, I have some dishes from dinner and I put them in there and add soap.
No big deal, right?
WRONG! I come back into my kitchen and there is soap all over the floor!!!!
I quickly grab a bunch of towels and throw in to soak up the mess and turn off the damn machine.
Mop, wipe, mop, wipe, mop.
Carefully open up machine. Soap bubbles. Full. Did I put too much soap in???
Screw this. I'll run it empty if I have to.