Why do you need to start with the clams partially opened if you're just going to steam them open anyhow? Thanks!

Normally you start with unopened clams and open with a clam knife, less work is to steam open...Sorry, but I tried another method once for partially opening clams and must have inadvertently referred to it in the recipe. The other method was to heat the oven to 475°, add the clams to an oven pan and pull them out just when the shell separates and finish opening by hand. Still more work than steaming them. Clams are so easily overcooked.