I don't see the harm in including that information. It would be one thing if you had a resume that was over 2 pages long, and you needed to cut down on the information. In this case, it doesn't seem like it can hurt to provide that information - and it might even be helpful. For example, I worked at a pet boarding facility for over three years. At first glance, that has nothing to do with psychology; however, during interviews, I was able to put a positive spin on it. You need to have good communication skills with co-workers and customers at a job like that - which is VERY relevant to the field of clinical psychology. I had to multitask - which is relevant to admissions panels for graduate school programs. Basically, I wouldn't suggest omitting that kind of information unless 1) it will hurt you more than it will help you, and/or 2) you have a limited amount of space on an application and need to highlight more relevant experiences instead.