I do for one simple reason. Disposals and Dishwashers greatly reduce the risk of clogged pipes. There are very cheap dishwashers so it's not a large expense either. When you don't have those 2 items, tenants tend to put bigger food items down the drain. At a minimum, an $80 disposal (maybe less) is WELL worth mitigating that risk.
I've been running a completely unscientific poll on our website,where we post info about homes as they're available for rent, for about a year now. It's a survey asking prospective tenants the feature for which they would be most willing to pay a higher rent. Options are: granite counters; washer & dryer; central air; dishwasher; none of the above. The overwhelming result has been the dishwasher (even over central air, which surprised me). For our rentals in B+ neighborhoods, we provide both a dishwasher and disposal. We also provide a manual for proper use of the appliances, and go over everything in depth at move in.
The duplex i'm putting an offer on in CT is .25 miles from the water in a very wealthy, white collar area. They put a new tenant in already and the floor she's occupying does not have a dishwasher. It's one girl living by herself, so she didn't seem to be bothered by not having it. If we get the place, i'll offer to put in a dishwasher for her if she wants to pay a little bit more. However, no dishwasher and no disposal in a high end area. I would be fine without both, it's a convenience thing, but not totally needed. However, I think washer/dryer is a must in a nice area, considering we don't have washer and dryers around the area I'm looking at.
A dishwasher is a must but not a garbage disposal. I cleaned a basement rental for four years in which the tenants clogged the garbage disposal sometimes. The homeowner knew how to fix the problem but he didn't have the time to correct the problem immediately. He installed a washer, dryer and dishwasher which attracted renters quickly so he had short vacancies.
Nick, as some above have suggested, you many be able to use a dishwasher or disposal as a negotiating tool. I had a solid tenant that wanted a dishwasher.i knew they were going to be in town for 3 years (doctor in residency) and so offered to give them a portable dishwasher in exchange for signing a 3 year lease. So far we are 1.5 years in and it has been great. Win-win in my eyes.