My situation is a little convoluted, but here it is for what it's worth. I was in two colleges, A&S and Music, and I was in the honors program. I had to be advised in both colleges before I could register, and it was in my best interest to pay a visit to the honors advisor before I registered for class too. Each semester I had to schedule three appointments for advising, and I thought that generally it was a waste of time.
My undergraduate school had a pre-med advisor that was useless and a big waste of time. They just recently added the committee letter to their services. This was added after I graduated but as I was reapplying. I didn't use either and I didn't have any problems, at least problems that I know about because nobody ever said anything to me. My school did, however, have a letter service that kept all my LOR's on file and sent them out to med schools at my request. I think it is a great idea to use this service if it is available because all your letters are in the same location and get sent out at the same time and you only have to ask the writer once.
Many med schools ask for or require the committee letter if it is available. If your pre-med advisor is as useless as mine, I would suggest you pay them visits so they know how great you are when it comes time to write the letter, but there may be other places to get better advice (departments, here, peers, etc.). If your school doesn't have a committee letter, you will be fine on your own as long as you keep focused and make sure you have all the prereq classes.
