It really depends on 1). Your chosen gear ratio and 2). where you are riding.
Some places have almost no hills so gears are useless actually, or almost useless.
Right now have all my 3 folders set up single speed, but that will change.
Single speed even worked in LA whenI rode up thru Cold water canyon everyday, it wasn't ideal but it worked well enough.
The ratio is a 55 x16 on 451 wheels. Works great most places: London- fine, Seoul- fine, Munich, Germany -good. Paris -great. Zurich , fine. In NYC the only places you really need gears is the bridges, but even then you can grin and bear it, which I did for 15 years now I run a 7 speed on my daily/non-folder The places you can't use it Lausanne, Switzerland (!) and maybe if I go back to LA I would bring gears to make it more enjoyable, still gotta figure that out. So it depends on where you ride really. The weight savings is good when lugging the case around in airports that as for sure.