What's the point of screen savers?

Well, I use a screensaver when I lock my screen to keep curious eyes off my screen when I'm away from my desk.

 

You could just turn the screen off. A screen saver may look better but just wastes energy and doesn't have a real benefit apart from the aesthetic.

 

The only way to turn off the Thunderbolt displays is to either unplug them or put the computer to sleep. When you have active tasks running, putting the computer to sleep is not an option.

 

Can't you use a hot corner to turn it off or the shortcut Ctrl+Shift+Eject (Ctrl+Shift+Fn+Power Key if your mac doesn't have an eject key)?

 

It's a throwback to the CRT days to help prevent phosphor burn-in if anyone else is wondering. Now it's used for aesthetic/personalisation purposes. Plus, I think some people still use CRT's because they prefer the colours presented by those displays. I suppose it can also be useful for in-store displays in Apple stores.
There the only reasons I can think of as to why it still exists.

 

If you are doing something, and you want to make sure your computer to have a completely black screen, than you can use one. Also, they look cool.

 

The phosphor burn-in explanation is correct. This was the original purpose for screen savers.

I still use one on my Macs.

I have hot corners set up in the Desktop & Screensaver preferences to turn on the screen saver if I put the cursor in the lower left corner. In the Security preferences, my system is configured to require a password immediately after the screensaver starts. Thus, the screensaver indicates that my screen is locked.

As for the choice of a screensaver, I think that's more a personal aesthetic decision than anything else. I have about twenty third-party screen savers that I've collected over the years. I change it up from time to time although my favorites are nostalgic ones like Flying Toasters and StonerView (a take on the SGI's Electropaint).

 

No hardware benefit. The UI benefit is that you can see that the computer is still running, not asleep.

 

I like the colors and the flying things <3

I don't care if I am wasting for 5-15 min. energy.

 

It harks back to days when most screens were TFT and the screen saver function did help preserve the life of the screen.
OS designers just kept that tradition up.

Secondly, it's for security reasons. In the same way that some organisations have a "clean desk policy" to prevent information leaks. A screen saver serves the same function. Imagine if you have an iMac at a hotel reception desk or bank angled so that the public can information. A screen saver can prevent the public or rogue employees seeing information they are not supposed to be privy to.