Id guess portability would be the only real reason to want one. That in itself is reason enough to get little refractor. In a pinch, you d be able to watch many things you would probably miss otherwise, just for not wanting to set up your larger equipment.
I know in a blink of an eye, I can have my small scope set up to catch a Lunar X event, or to look for new sunspots when I get an alert from Spaceweather.com.
Someone might mention an object they observed last night and it would spark my curiosity to take out a quick high quality grab and go scope and locate that object also.
I might be on my way home from work and notice a sliver of a crescent moon, and want to get out the quick scope and take a look.
Right now, Venus is in the west at Sunset, still high enough to get a high quality view of it. The small Tak would be excellent for that.
The reasons for wanting a small portable refractor are endless.
Sometimes, I go out with my small set up to look for one object of interest. I may walk through my favorite messier objects also. Without a small quick set up. I would probably miss many nights of observing.
Its good to have the larger gear for a full night of observing. Sometimes you just want to get your astro fix and are happy to take out a quick set up for an hour or two just stepping out your back door. A small refractor would make you a more complete astronomer, and get you out more. You would be out much more in the winter time, on nights of clear skies.
I use my AT-92 as my quick back yard scope. I also use a CG-4 on a light weight vixen tripod with a small mounted tracking motor on it, running off a 9v battery. In 5 minutes, I can go from reading an article on CN's to being set up and ready off my back patio.
I need a tracking motor. I like to get above 100x on double stars, when looking at specific sites on the moon, or for planetary observing. For me, without tracking, high power is limiting. My entire set up, mounted with eyepieces and counterweights is under 30 pounds.
Plenty light enough to carry as a complete package anywhere in my yard.