I have a lot of old consoles ranging back to the Magnavox Odyssey 2 so I always keep an SDTV and a back-up on hand for those (Specifically, a 30" Toshiba from 1992 and a 28" RCA Colortrax from 1984. Best SDTV's I ever owned).
My PS3, Xbox360, Wii and the computer I'm using right now all run through a 40" HDTV. Kinda stupid though that people will waste the time to insult the VHS format, we only had to use for over 2 decades. I even have the most recent VCR that JVC made (2007) hooked up to this TV for viewing my old tapes, they look so much clearer on a HDTV. Why would I do that? Because there are tapes that I own that have still not made it to DVD, let alone Blu-Ray. Some are rare gold, some are weird shit, some are humanly insulting but that's the appeal to them... get some friends around and blow their minds.
And something unrelated but even more hilarious? I have a Vinyl LP of Dutch porno from the 60's. That is, it was a reel-to-reel film that needed the record's audio to play in sync with it for the full effect. Sadly, or thankfully, I don't have the film to go with it.
But back to the SDTV thing... yeah, don't ever hook up an NES or Atari to an HDTV. If you do, you'll know why. Get yourself an old TV for cheap from a Flea Market that works reasonably well if you want to play those things. Probably the best reason to still own one.