anything over 1.060 you'll absolutely want to do one. Under that, you're ok...
That's just wrong. Like DrunkleJon said, check mrmalty.com every time. If I go there right now (
LINK for the OP) the default screen shows that for a 1.048 OG ale, with an unrealistically fresh pack of liquid yeast, you still need 1.8 packs or a 1L starter on a stir plate.
If you want to ignore the experts' advice on pitching rate, that's fine, and it's completely your decision. That's an argument that's been beaten to death on here (whether or not the proper pitch rate makes a noticeable difference), and there are many people that underpitch routinely and still get excellent beer. For me personally, since it's one variable I can easily eliminate I pitch the proper amount. And a faster start is always a good thing, since it minimizes the chance of infection.
But to directly answer the OP: unless you brew very low gravity beer, or you you brew smaller batches, or get your yeast the day it was packaged at the lab, following proper pitching rates will almost mean that you need a starter every time with liquid yeast.
As mentioned, dry yeast has a much higher active cell count to begin with, and it stays much more viable during storage. You can check the same mrmalty.com calculator for dry yeast, but remember that's assuming you're properly rehydrating. If you aren't, you might want to double what he recommends.