Since I LIVE in Cuddl Duds YEAR round and essentially every one of their shirts has thumbholes, I will say Yes, they serve a purpose! I use them if my hands are cold, they are also very convenient if I have to put a jacket on over the shirt as the sleeves don't "ride" up this way.
I don't see why anyone would have an issue with them, they are there if you need them and if you don't just don't use them. Pretty simple :-)
~ Hope in TN ~