You can use both types for thinning some acrylic paints, but make sure you check first. Paints are best thinned with the apropriate thinners(same manufacturer thinner), but IA can be used to thin ones such as Tamiya and Gunze. Don't use it to thin Model Master or Floquil Acrylics.
I've never heard of using IA to remove putty, and it doesn't seem reasonable since it has no effect on putty. I heard that you can thin Squadron putty with alcohol, but I tried both Isopropyl and Ethyl to no avail. You can use finger nail polish remover to remove toulene based putties such as Squadron, but in my opinion it doesn't work very well and just smears the putty around. You should use finger nail polish remover with acetone, but I have heard of people using the kind without acetone.
It would be nice if Squadron putty was slow drying so you can easily clean it up. That's why I use Model Master Red. Plenty of working time.