Years ago I had a nearby lightning strike fry most of my house. Near as I can tell if came in on my phone wire though... Killed my phones, television, ham radios, garage door opener, the low voltage lighting in my front yard, and my personal computer.
With that experience in mind I decided to get one, as well as for reasons stated above (brand new camper with lots and lots of electronics everyplace.) The entertainment system, microwave, furnace, fridge, AC, converter, you name it, and it seems to have a chip in it nowadays. I won't say I bought the absolute top of the line unit out there but not the cheapest either... I know much of this runs on the 12v system but still...
If we are talking about a much older unit with less electronics then you might be ok to skip it... Maybe.
I know lots of campers out there do not have one and never had an issue. For myself I figured the way my luck runs I'd better get one. ;)