Low torque is the key. I don't own a set of ball-end allen wrenches, but if I did I would only use them for things like bottle cages (low torque, plus odd angle sometimes necessary). I especially wouldn't use them on a stuck fastener that is at risk of rounding. With things like this, if I own the tool I tend to use it when it sometimes is not appropriate. Like when working on the car I'll grab a 12-point socket just because that's the first thing I lay my hands on, rather than get the 6-point socket to use on that rusty bolt that might round off.

-Ken