With a Server header that long, shortening it or getting rid of it entirely could also provide a tiny performance benefit.
As Jesper notes, it's not a big issue, but if you're trying to squeeze out every extra millisecond from your page load times, it could make a difference — particularly if you're loading lots of small files, which is bad from a performance viewpoint in itself, but sometimes unavoidable.
I suspect that's one reason why, for example, Google's webservers just say:
Sure, they could've spelled out "gws" as "Google Web Server" without disclosing any more information, but that would add 14 completely useless bytes to every HTTP response. With Google's request volume, those few bytes might well add up to more bandwidth than your average small website uses in total.