If we're going to have a bunch of kids swimming, sometimes I put boost on in the morning and turn it off after swimming, adding to the normal chlorine production. For example, turning it on at 10 am and off at 6 pm adds 3 ppm to the 2.5 ppm the SWC would normally make per day. If I forgot to do this, I'd pour in a quart (litre) of bleach which does about the same.
If I just hit the button on mine and let it reset on its own, it runs at 100% for 24 hours, making an extra 1.1 lbs (500 g) and delivering 11 ppm extra. If I did that weekly, assuming cell life of 440 lbs (200 kg), it would use up the cell in ~3 years instead of ~5 years. So for me, that's a reason not to do it! I've heard the weekly shock recommendation several times, but not backed up with any real reason for it.