When I am working on stuff and I have been doing lots of things without a save I really really start to get the creeps. Its like I start to press each key stroke carefully etc. My threshold before this starts to come on is about a few minutes. This is especially true if doing art but I even get this when typing in code which in theory should be easier to repeat. So to go several hours of artwork would make me feel like I was standing on the high wire at the circus. In the old days we used to have computers with no hard drive and before the floppy you used to have to have a cassette recorder to back up a program. When the (very small) power lead used to wobble then it would crash the machine and wipe the RAM. There was a point in time when the computers had enough RAM - about 16K of it at the time but before the floppy disk - when you could spend a few hours typing in hex codes from a magazine to program the machine in machine code to play a half decent game. A crash during that period would wipe out several hours. I think I developed my creeps during those early days. Now that the HDD makes saving so easy I use it all the time.

You should have a play with MeshLab and do some 3D modelling. That program will crash every 30 seconds. Its amazingly poorly written even if it is doing some excellent processing and implementing some extremely useful stuff. Tho I grit my teeth against this one app, on the whole tho I avoid all crashing apps like the plague. I just cant bear it.

Just to hammer it home some more. I save often. I save with increasing number appended to the end. I.e. I don't keep saving over the top of an old version. And when you have done a few of them and what you have is worth something then copy the whole directory to another. It might be a waste of HDD space but its your time and effort here. If HDD space is worth more than your time then go an do something more worthwhile cos HDD space is cheap. A 5Mb map save is about 0.01 cents.