Question about buying concert CDs

Random question but - if I buy a CD from one of their shows - it's just audio, right?

I guess their tours are only sold in "audio" format, and there's no way to watch them other than select shows they decide to release in "video" format, right?

Also - going to the metallica shop, I see some CDs of shows being "sold out", but when i go to livemetallica shows it seemingly lets me buy CD versions of shows? Is this a mistake and if i try to purchase them it will tell me it's not available?

Also, what's the difference between buying a CD for a show instead of just purchasing the Mp3 (or is FLAC better? i don't know this stuff) ? Is there a bonus or something or it's just having it in a physical form that's the selling point of the CDs?

Sorry if this post seems a little hectic