just like Jim says in the first paragraph of the article, its one of those things that with time, you just know when its time to back off. when you are first starting out, everybody is so eager to make huge gains, yet they forget about the fact that rest is needed. same thing with injuries. so many people new to the gym think that they can just work through something. and again, what they really need is rest. before you really hone in on your training, and know you body, you have to force yourself to take some time off every so often.
typically, I will take some time off (not really off, but back my training off a few notches) when i stop making steady gains, or after I make some huge PR's. right now, I'm about due for a back of period, but I have to keep pushing a little, as I'm getting ready for a meet in June. i'm getting some new gear, and I have to do the best that I can to learn the groove of the shirt, and get used to using my DL suit. after the meet, I will be taking an entire week off, and then take a few weeks to get back into the swing of things.
the same thing with injuries. you can't work through them. you can't continue to go full bore when you get hurt. workouts need to be heavily modified, and scaled way back when you get hurt. this is something that most people only learn once they have screwed them up pretty badly, and have been forced to take months off from the gym, instead of a few weeks if they had simply taken time off, or heavily scaled their workouts back. b/c of my back injury last year, at the slightest sign of something that hurts during a workout, i call it quits for the day. and if it doesn't feel right the on the next workout day, then I'm either not working out, or I am doing significantly less work (weight wise). there is no point in pushing yourself once you are injured. be smart about your training, and take time off. a couple days off, is much better than a couple months off.