It does help if you do put dates, because potential employers will want to know one way or another. They'll likely ask you in the interview.
Most don't ask tho. My mate does it due to him being off ill for 5yrs. He hasn't even been asked when the last time he worked. They just asked him about his jobs etc.
When I was shown how to carry out a interview I said should I ask about the dates they worked. The answer was no, aslong as the job list helps them to get the job they are after it doesn't matter.
Plus if I am seen as turning a person down for a job that hasn't worked for a time(for any reason) I could get in trouble.
Most places now don't even phone up your last place of work.