In the past, I used to not care, but now I prefer when there are tour dates on the back. It isn't a make or break decision, but I'm more likely to buy a shirt if it has the dates on it.
7/19 - Megadeth
8/11 - Swashbuckle/Crimson Shadows
8/20 - Skid Row
9/5 - Spell/Manacle