So I've been playing Mass Effect 2 (PC) and one of the things I've noticed is that you can only save your game when you're not engaged in combat. As soon as the first enemy shows up on your radar, the save button is disabled. Once combat is over, save functionality reappears.

It seems reasonable to assume that Mass Effect 2 is a state machine, and therefore, the internal state of the program at any moment can be captured and reloaded later. This is basically a solved problem - games have been designed this way since the Half-Life era. It also seems reasonable to assume that BioWare knew what they were doing when they made the decision not to follow this model - it's a tried and true system; BioWare wouldn't have done it the way they did without some good reason.

What reasons are there to disable game save functionality during combat?