I shoot transparencies, and usually just slot them into negative filing pages unmounted.
A while later I may mount 35mm (I do this myself, lots of mounts on hand and the gear to use them).
MF get scanned if the urge siezes me.
4x5 I put into black matt mounting outlines and an acetate sleeve and sit on the window sill. People see a 4x5 transparency and say wow most of the time.
I also shoot spluges of 35mm and 4x5 copy camera work as a way to document old paperwork or artwork things from around the house that we want a record of, but to free ourselves of the actual original. An old Polaroid MP3 copy camera with lenses to cover 35mm and 4x5 with good 4 way copy lights and a 20x24 glass platten is a big help in this respect.
A bunch is ephemera- theatre production posters, programs, cast listings and thank you cards from a particular production. My wife and I have done over 50 theatrical productions between us in community theatre within the last 15 years, and the momentoes boxes were starting to seriously overflow.
I also shoot in the copy camera or with a bowens illumitran, quite a stock of old 100' bulk reel stocks of e-6 dupe films and c-41 interneg stock. Once the corrective filtration and exposure is dialled in for each particualr stock the results are amazing.
Sometimes my duping is done to reinterpret old slides. Sometimes it is to add a new generation onto to the best shots of a carosel of color shifting aging Ektachome or Anscochome slides from decades past. Once the major fade colur shift bias is mostly compensated away from with judicious filter your eyes and brain doe quite a good job accepting the reduced information that some colours carry.
I do confess turning to the scanner as a quick way to pick the right mix of compensating gelatins prior to then loading them into the duper and copying the old stock.