One place I applied to 'hmm think we toss it onto sourcesafe once and awhile'. It was their main product. They had about 15 people working on it. Plus one big ol folder on that one machine that was 'the builds'.

Some slight rigor shows you are not just doing whatever. I found most projects once you scale past 2 or 3 people and your 3rd release you basically are forced into some sort source control. Or it is a game of 'what file did they break today and I have to spend 3 hours fixing before I can add my feature'. Then you end up with merge meetings and very weird things happening.

Usually missing source control in an older org means there is a large swath of tech debt. Watch for the weeds. You will find other things very quickly.