I agree with you that it isn't strictly speaking necessary, and that the speeds won't drop so much so that the drive becomes unusable or HDD slow, and you especially won't see that great a difference when you're already most likely bottlenecked by SATA II. All that said, as
@Weaselboy also points out, when it's there, easy to activate, and does no harm but only optimises what you have, why not take it? For your data accesses you may feel literally no difference at all, but back before I switched to iMac, I did notice the difference for my Final Cut usage, when Apple released their official trimforce, and I finally bothered activating TRIM on my aftermarket SSD. Working with larger projects just became that bit more smooth.
Anyway, as with anything YMMV and you could have the same experience as
@xWhiplash. I still recommend activating TRIM however, as it's easy, can't harm, and even if you don't notice the speedup, you're allowing the drive to more intelligently manage itself internally, potentially increasing the lifespan of the drive, since it'll be more capable of performing what is called wear-levelling. This effect should theoretically be extremely minimal, but just another good reason to have TRIM.
