I guess it depends on the condition of your back. I would say not a necessity, but sure nice for a long trip. I have the Utopia, lots of passengers complain about the types with external bars - gets in the way.
I don't like back rests, but back pain on longer rides convinced me to try one and I gotta say it really helps. I installed a removeable Utopia on my 1500. Easy installation. I had one on a Saddleman Road Sofa but didn't like the seat so didn't use that back rest much before putting a new OEM seat on my 'Wing.
My 1200 Aspy is the first bike I've ever had with a back rest. I got used to that REAL QUICK. I really like it, especially on longer trips. The only minor drawback is - the back of your shirt gets sweaty in the summer from that area not getting any airflow. The advantages far outweigh a little back-sweat, IMHO.
The 1500 I'm working on has a Travelcade RoadSofa on it, but I haven't had the opportunity to put a good ride on it yet to see if I like it. It seems firmer, and the bucket seems deeper than the stocker. We'll see.
I've already had surgery on my lower back long before I got my wing and a back rest is the first new part I bought for it. It saves me a lot of pain when I ride 1-up. It comes off in 2 seconds for 2-up riding as like mentioned, the side bars interfere with the passenger.
When riding two up my wife is my backrest, actually she likes being able to be close to me so says leave the backrest off. When riding solo I use the backrest it is adjustable front to back and I find it great add on and if riding solo on long run would greatly miss it if I didn't have it. By the way we have a Heartco presidental seat and love it. Another comfort thing for long runs is highway boards or pegs, I didn't care for the looks of them until I used a set of highway baords now I'm a believerat 6'4" I can get cramped on just about any bike.
I just last week bought a 1500 that had a markland backrest on it. Took it off the first day. Kept me too far forward and limited my wife's passenger space. The chrome bars do make it easier to put the bike on the center stand though.
I hadn't had a backrest on mine for 17 years, and struggled constantly with finding comfort while riding distances of greater than 100 miles.
Last year I bought a Saddleman with backrest from a forum member here and have since wondered why I didn't do so sooner. It's so nice to be able to put my feet out on the cruise pegs, lean back, and just goooooooooooooooooooooooooo.
my gl1500i came with a backrest when i got it, just 1 post mounting through a hole cut in the middle of the seat. i have test ridden stock gl1800 without the backrest & my neighbor's harly road king without a backrest & maybe because i have always had 1 i don't feel as comfortable without it. i find that wheni accelerate it feels like i'm going to fall off the back of the seat unless i firmly hang onto the handlebars without the backrest, but with it i stop from falling back so i can loosely hold the handlebars & be more relaxed. i also on long rides will wedge my feet against the highway pegs & my back against the backrest periodically for a few minutes to get my sore but off the seat which helps me go longer without having to get off & walk around as often.
Started out on my 81 without, now have one on the 81 and 82, and I'll give 'em up when they pry my cold dead hands from them:cooldevil::cooldevil:, I used to get a burning sensation between my shoulder blades after riding for a while, now with the back rest I can ride alot longer, and it does not bother my back.........LOVE 'EM!!!!