Is there a difference between boiling water and almost boiling water?
There are two main differences, obviously: five degrees, and no boiling action.
As Cascabel mentioned in a comment, dried pasta will &quot;cook&quot; even in water that's well below boiling temperature. However, a rolling boil serves to constantly stir the contents of the pot, much more than convection in heating water would. Without that mechanical action, pasta is more prone to stick to itself and to the bottom of the pan. So stir a few times.
For fresh pasta, it's more important to use boiling water (and lots of it), because adding the pasta to the water will significantly cool the water below the point where the pasta can actually cook. The sticking concerns apply even more there: fresh pasta has more loose surface starch to cause sticking if you don't stir.
Incidentally, you mentioned in the comments that you assumed it was slow to bring water to a boil &quot;because of the phase change involved&quot;. But there is no phase change involved below 100 degrees. In an uncovered pot, it takes a while to push water from a bare simmer to a rolling boil because the evaporation cools the water more quickly as the temperature increases. Covering the pot will significantly decrease the time to come to a full rolling boil (or to return to the boil once you've added the pasta).