Is “Save As” safe?

I often use Save as... It's how I make back-up or I use it when making a video and I'm doing changes to a sim or household that I don't want to be permanent. I have tons of saved files in my game, but I include my year count in the names so I can easily delete those that were meant to be temporary saves.

I never had any trouble with this, but I recall there was some warning against "save and quit", but that might have been back in TS3 for a limited period... not sure.