I think it helps to support the weight of the head which can be about 8-12 lbs, so it lets the neck muscles relax a little bit.
Short term as needed during bad times to take some strain off the neck should be oK, but not a constant or long term thing for the reasons stated in the earlier posts.

I had finally got one for long car trips or bumpy roads , but didn't use it much, but keep it just in case...along with all my splints, elbow pads & helper stuff.