I only skip socks if I need shoes for a very short trip (basement, garage, etc.). Otherwise, I always wear socks and shoes because it's more comfortable than just wearing shoes.

I would not wear socks with sandals or surfwalkers.

Ah okay that makes sense really

Well, I never wear socks with shoes like flip flops, sandals, heels and so on as it either looks weird or feels rather uncomfortable. Or both, for me at least.

As for flats and chucks and sneakers, I usually do wear socks. With first two kinds, I prefer wearing some low cut socks, though.
If I want to put on such shoes on without socks, most of time I'll just wear some old pair. In fact, I've two old pairs of chucks that I never wear socks with.

Heels, sandals makes sense without socks

I'm surprised you wear them with flats though

A lot of people I know do, actually. While I certainly wear socks with flats way less often than I do with eg. sneakers, I still wear them like that.
Most of time it's rather difficult to tell whether one has socks on or not, as long as they're low cut socks, without staring.

I'm the same way! I'm usually wearing socks.

I have a keen eye and generally can notice if socks are worn with them kind of shoes

Maybe that's just me though

Yes that's the type of socks I was assuming alright