This depends on how your letters are being submitted. ADEA AADSAS allows you to upload up to four letters. Some schools may even ask for individual letters separately. I used 7 strong letters. 3 of them I gave to my pre-health committee, and the additional 4 letters my pre-health advisor offered to attached to that same packet.
If you are in a situation where you can submit another strong letter, then I don’t see why you shouldn’t.
I also got 5. So, I packaged 3 with the pre-health letter and two separately.
Some schools may have additional requirements. E.g Rutgers wants 3 faculty letters. If you have an extra letter, you can simply forward it to them as opposed to sending to all schools through AADSAS.