I spent my entire Saturday sitting on the middle step of my main staircase trying to sand eighty years of dark brown paint off the wooden risers. I bought a massive bulk pack of generic sandpaper from the hardware store last month because I thought I was being smart about my budget. The pack cost ten dollars for fifty sheets.
It took me exactly twenty minutes to realize why it was so cheap. The backing paper is incredibly thin. The second I started pressing into the corners of the stairs, the paper completely tore in half. I tried folding it over to make it thicker. That just made the grit rub against itself and flake off onto the floor.
The real issue is how fast it clogs. The dark brown paint on my stairs is likely oil based and extremely thick. One pass with the cheap sixty grit paper and the entire sheet was coated in a shiny brown residue. I had to throw a sheet away every two minutes. By noon there was a pile of useless torn paper sitting on my drop cloth.
I finally drove back to the store and bought the expensive purple ceramic sandpaper. It costs almost twice as much for a fraction of the sheets. It is completely worth the money. The backing actually holds up when you fold it into a sharp crease to get into the trim profiles. It still clogs eventually, but I can actually get an entire stair riser done with one piece.
If you are sanding anything older than twenty years, skip the bulk packs entirely. You just end up spending more time changing the paper than actually sanding the wood.