I leave the economy on, because I like having shops and I _really_ like not having to manually assign every friggin' one of my 200+ bedrooms. But I turn off rent because it makes no sense whatsoever to have half my fort homeless while a hundred perfectly serviceable bedrooms sit deserted. There really needs to be some supply and demand in that. I never make coins.
Anyway, I will sometimes savescum when my dwarves do something mind-bogglingly stupid that no sapient creature should have done, like wall themselves up and starve to death. I've savescummed a few times to save a megabeast I want to capture alive, too; I justify that by the fact that megabeasts are irreplaceable. If a dwarf gets a mood that could produce something of practical use, like artifact furniture or armor or whatnot, I'll make liberal use of forbidding from the stock screen to ensure that he uses the best materials. I've used quantum stockpiling to clear away the boulders from my tower cap farms in the past, and in my current fort I've got a steel atom smasher for garbage disposal (Goblin crap was flooding my stockpiles and it rots too slowly when left outside). Another method of rock disposal I use that seems a little bit exploity is to turn it all into constructed floor in the same tiles it was mined out from. Especially handy for water channels but it's weird that I can pack all that rock into the floor like that.