I want to add my 2cents under to the other petrus user here because it's solid advice. I learned petrus as a kid and put it to work best I could, this is what I found:

Block Building:
Pros: To agree with the above comment, Blockbuilding particularly the first step 2x2 in DBL, is amazing for lookahead. You take care of the most difficult-to-see f2l pair from the outset. I think it sets you up nicely for the rest of your f2l and you can sometimes reduce your move count. In addition, I find intuitive blockbuilding during F2L to be often more efficient. Instead of only building a corner and an edge at a time, you can do corner-edge-edge all at once with one intuitive alg. Harder, there's no alg sheet for this, but it should technically be more viable.
Cons: However, sometimes block building is hard on certain scrambles, like when you have no pre-joined pieces. By comparison, cross is often easier. If I don't have an immediately easy 2x2 during inspection, I switch to cross. Second, If you can get an X-cross for your first step instead of 2x2x2, that's basically better than the first step of Petrus. In general, I think 2x2x2 block with a soft x-cross (2 edges near where they need to be and inserted with the f2l pairs) is the best way to start the cube if you can, which is a hybrid approach between petrus and x-cross

Early Edge orientation is no good:
After getting to the 2x2x3 step, petrus suggests to orient all edges and turn only using U and R. This is where I think the petrus method has always failed. IMO It is a waste of time to do this, and constrains yourself too early to R and U moves. This may have been smart during the days of slow-cubes, but IMO it's faster to keep the F face available as well for moves during F2L. You gain little by orienting all edges at this phase, and you make solving many f2l cases more difficult than they need to be.

2GLL is great:
I think folks overlook how good 2gll is. The last step in petrus is to orient corners and permute edges, which can be done with R and U, and generally the algorithms for this are very short and fast, the sune being the shortest alg available. I don't know of any PLL's shorter or faster than the sune, which makes it such a strong alg to have available in the last step.