Is this a pre-med letter writing committee? If so, then yes, absolutely get a letter from them. Many med schools request a committee letter if your school has a pre-med committee, and it might be a red flag if you decide to apply without such a letter in that case.
The way my school's committee worked was that I was responsible for getting a certain number of letters from professors on my behalf. Our committee recommended getting two science and one or two non-science letters, one or more letters from PIs, and a letter from a significant extracurricular (i.e. coaches, volunteer coordinators, etc) if we felt it would show a different side of us than our other letters would. Letters from these sources were sent directly to the committee, and the committee went through and highlighted the particularly strong points in a type of cover letter. The committee also included information that they had gathered from our records, from personal interviews, from a series of essays we had to submit to them, and from generally knowing us on a one-on-one basis; the aim of such a letter was to capture our personalities, interests, achievements and potential. The committee letter was then bundled with all my other LORs and was sent to AMCAS and non-participating med schools as a packet.
There are many advantages to using a committee letter, and I can't think of any disadvantages (especially when the committee letter is used in conjunction with the individual LORs). Each med school has their own LOR requirements, but all of them will accept a committee letter packet.
In your particular case, I'm not sure if what you have is a pre-med committee or not. If the letter just represents the opinion of the biology department, you'll likely still need to submit non-science letters and the like.
