I'm currently doing Stronglifts 5x5, and I've read a lot of material about strength training. Everything I've read so far indicates that sufficient rest is essential to making progress and building strength. All the reputable lifting routines prescribe "rest days". Stronglifts and Starting Strength both say not to work out more than 3 times per week.
The theory as I understand it, is that your muscles break down and weaken after you use them strenuously, and then "bounce back" over time. If you time your workouts right, you can train during a period where your muscles are overcompensating for the damage you've done, and you'll get a boost to your next workout. But if you train too soon, your muscles won't have recovered from the damage done, and you'll just be tearing them down again, preventing progress.
Ok, sounds reasonable. But here's where I get confused. I've been looking into ways to train myself to do pull-ups and chin-ups. At present, I can not do even one rep. One method that gets mentioned a lot is "greasing the groove" or "greasing the bar". Some people advocate putting a pull-up bar in a doorway in a frequently-used part of your house, and doing one rep every time you pass it. Other people suggest doing a certain amount of reps (or attempts) every single day, or at least every workout, until one is able to do a few pull-ups.
Based on the anecdotal evidence I've seen, "greasing the groove" sounds like it works. But how could that be? If I'm straining my muscles doing negative pull-ups or negative chin-ups, and I'm doing a rep here-and-there throughout the day, every day, when would my muscles have time to recover? Wouldn't it be the same as if I were doing squats or bench pressing every single day - overtraining and preventing progress? How is it possible that rest days are important for some exercises, but constant every-day effort would work for chin-ups/pull-ups? Can these two lines of thought be reconciled?