While most Aura cards are generally used to buff your own creatures, there are auras you want to attach to opposing ones
In that case, you can only subtract 2 tix from the selling bot, and later, if you want to use just a fraction of those two tix, let's say 1.5 in another chain like Goatbots, the bot will keep 0.5 as credit that you cant subtract unless you use it to get new cards
Still, its not so amazing alone to make it essential
5 Time Walk Rare - $7,700 Time Walk is one of those Magic cards that just seems too good to be true, which is why Magic doesnt print cards like that anymore
Just look at this short list of what you can get back, from the top of my head: Zulaport Cutthroat Cruel Celebrant Corpse Knight Elas il-Kor, Sadistic Pilgrim Bartolom del Presidio Blood Artist Viscera Seer Carrion Feeder Marionette Apprentice Reassembling Skeleton Putrid Goblin Cathar Commando Cast Raise the Past, sacrifice your entire board in response, and get them all back none the worse for wear