Except that it may be the only way you will get the latest security updates quickly. But I understand your hesitation. I think Lollipop was a tough upgrade all around for many devices. From what I have read, Marshmallow doesn't seem to be causing nearly as many problems. I myself will wait a month when 6.0 comes out for my phone, then do a search for problems on my phones before doing the updates. If it seems acceptable, I will upgrade.
No way to know until it comes out and we see feedback. Unfortunately, for Samsung, they have a lot more bells and whistles to make work.
As to the basic question of who wants it. Well, I think the real question is, who doesn't want it. You say now that you are happy with L, but tell me you won't be excited when it actually comes out.