[cmontella]

It can work but it depends on the system. One field in which it's very useful is game development. I'm working on a language that has time travel debugging as a feature, so you can rewind a game back to a previous state. I've found it useful when there's a momentary bug that would be hard to recreate. With time traveling, you pause, rewind, inspect state, fix the bug in situ, then resume from that point to check that the behavior is correct.

Here's an example: http://docs.mech-lang.org/#/examples/bouncing-balls.mec

If you want these kinds of features in other systems, they'll have to be architected to support them. For example, the external database will have to be rewound as well. If it doesn't support that feature, then cool language-level debugging features won't be as useful.