Not needed at all. UNTIL your fridge gets blown out and the transfer switch gets damaged due to a nearby lightning strike. A new fridge cost me $1400 and the tech who "saved" my transfer switch charged me another $186. And this is ONCE after 25+ years of camping. (Never "needed" it before)
THEN.....reading up here on this forum, I decided to go with the Progressive Industries PORTABLE 50 amp unit. From Tweeteys' on the net. At the time, maybe $325. A bit more on the Progressive site. Now...everytime I set up, it's part of the setting up. And, altho here, you might read that portable units are victims of theft, I really find theft is not an issue. It's always "happened to someone else" or "a friend of mine". Never to them that write about it. So...you have a choice. Hard wired in or portable. I like Progressive...a LIFETIME warranty and they respond to your e-mails of any concern. And you can "step down" from 50 to 30 to 110 with adapters if needed. Works fine.