Increasing intensity for subsequent sets?

[DORKtoDIVA]

In the Body for LIFE book, he describes doing one set of a given exercise with one weight, then the next set with a higher weight, and so on.

Currently I had been doing 2 or 3 sets (depending on the exercise) with a goal of 12 reps, but with the same weight for each set. If I hit 12 reps for each set, then I plan to increase intensity next time.

The book doesn't describe (at least that I saw) what increasing the weight for subsequent sets would acheive. Also I didn't quite understand how I'd determine those intervals. Anyone have any light to shed on it?

My goals are kind of murky and all over the place, but I'm not afraid of "bulking up" or anything. I just want to be stronger and more fit and look better.

I think I'd rather not keep increasing intensity; it takes me enough time as it is to do the workout, it sounds like it would take me three times as long to always be changing the plates even between sets. So unless someone can explain why this method is vastly superior, I don't think I want to do it.

[Trusylver]

Pyramid sets are a good way of building strength but are not needed if you are a beginner, 12 reps puts you in the zone for building muscle size rather than max strength.

I use pyramids for biceps at the moment but not for my other muscles.

my bicep curl pyramid looks like this

10 @ 12.5 kg
8 @ 15 kg
6 @ 17.5 kg
4 @ 20 kg or failure whichever comes first

if i fail on the 4s i will repeat the following week if not i will start with 15 for 10s and again pyramid up.

I also cycle the intensity of some exercises with intensity rising each week for a few weeks then dropping back down so the cycle can start again but at more intensity then at the same stage of the last cycle.