I absolutely agree with it. I actually learned that concept from a post here where a couple of more experienced traders were talking about pretty much the exact same question. If I get a few minutes later I'll try to hunt it down.

I think a lot of resistance and support is pretty much just guides. People making sense of something that makes little sense and so long as everyone is using the same guides, that in and of itself adds a certain level of predictability.

It's kind of like saying: people are selling long positions for profit at resistance because they're scared it won't go higher. But, assuming they don't have any position in the stock as per the previous sentence, if it breaks through resistance on decent volume, they'll wait to see if it comes back down to that newly created support to as an entry point to go long on a bounce.
I think it's just whatever fits into their strategy. The most important thing though is actually having a strategy. I am still learning but another thing I read here from a much much older post was "Choose on fundamentals, decide on technicals." and I definately like that. I may be naive, but I wouldn't really want to trade just solely on technicals. I'm sure it's possible, but I need a more solid reason.

And I'm confused why people even care about support/resistance from years ago that is likely based on something completely obsolete to the present.
I'm sure it depend on the stock and the inteded way to trade it, but that does sound weird. Where did you see people using this?