The Ninjask in my backpocketThis also brings me to another point which I didn't fully appreciate when I was starting. Dragon Dance Tar is immensely immensely threatening because it outspeeds the whole tier at +2 and can only be reliably stopped defensively by swampert (and to a lesser extent flygon and some other rarely seen options like donphan or whatever). An extremely common way games end in ADV is Tyranitar gets an entry on a mon that can't deny its setup, it clicks dragon dance as opponent switches to a soft check, it dances again and lives a hit or clicks rock slide and gets a flinch --> sweep.
Another thing is that by running Tar you pretty much invalidate a ton of the idiotic "Time wasting teams" without a clear wincon that you see every 50-100 games. Sandless+spikeless have to sit for ages against them. While that doesn't make Tar better exactly, you feel damn glad that you brought it around.I also just want to add one more thing about setting sand. It is hard for a team to be extremely consistent, i.e. not have any wacky set that just 6-0s you from the start, if you don't have sand. Sand is the thing holding back a lot of things that would otherwise be giga threats like pinch berry reversal/flail sweepers, subcm suicune, curse rest lax (honestly all suicune and lax sets to some extent), rest zapdos, etc. Now, I'm not saying it's impossible -- and there are certainly notable players who load a lot of sandless to success. But for a lot of players they'd rather just load tar which is a perfectly good and solid mon than play GSC lite for 500 turns or randomly get 6-0'd on preview from some cheese.