Just my incomplete list. I use n900/maemo every day and believe it's more useful than Jolla/Sailfish. Its main disability is weak hardware.

* Run desktop apps like pidgin.
Sailfish can run desktop Transmission with qt frontend.
Maemo is able to run Pidgin. I want to run pidgin, even though it's not optimized for mobile use. I would like to have possibility to feel the power of fully fledged operating system.

I run pyobd on maemo.
I check my car with pyobd. I cannot do it with Sailfish.

I write GTK apps, compile them in scratchbox, and they work on maemo, without hildonization. Just work.

* Take RAW pictures.

There are only two native cameras for sailfish. I have no idea if Sailfish API allows to take RAW images.

FCamera application is just great on maemo. I still use it, and get much better results than Sailfish/AlienDalvik/Instagram.

* Know the name of radio track.
Sailwave description states that because of some qt bug they cannot implement it yet. So I listen internet radio and have no idea which song is broadcasted, so I can find it later.

* has more useful apps which are very hard to port to sailfish because they are not qt.

* has SIP out of the box.

* has Mappero, I did not find comparable program for Sailfish.

* resistive screen
This one most of you won't agree with but I really prefer resistive screen and stylus. I want to run MyPaint. Yes.

* connect to WPA enterprise out of the box.
My maemo's connect to our company's wpa enterprise spots but I had to manually edit files on Sailfish as root.

* external bluetooth keyboard cannot be used with non qwerty layouts. I use dvorak or programmer's dvorak for Latin, and I also use Armenian typewriter layout. It's not possible with Sailfish yet.

I certainly don't remember many other points and may add later.