Caution, Captain Obvious here.
Like most on this forum, I've tried pitching hydrated dry yeast and direct pitching dry yeast, and have a personal preference, but if an inexperienced brewer is reading this, you might be well-served to try both methods and decide for yourself if the time spent to rehydrate the yeast is worth it to you.
FWIW, regarding dry yeast suppliers official position on direct pitching, I found this just now on Lallemand's website:
Upon rehydration, dry cell membranes undergo a transition from gel to liquid crystal phase. Rehydration in sterile water is recommended prior to pitching into wort in order to reduce stress on the cell as it transitions from dry
to liquid form. Proper rehydration of dry yeast will produce a highly viable and vital liquid slurry.
However, digging a little deeper into their technical data sheet for Diamond Lager this is found:
DIRECT PITCH "no rehydration" Sprinkle the yeast evenly on the surface of the wort in the fermenter as it is being filled. The motion of the wort filling the fermenter will aid in mixing the yeast into the wort.
So their recommendation remains to rehydrate before pitching, but then they explain the process of direct pitching, although buried a bit in the data sheets. From memory, Fermentis has similar verbiage, or at least meaning, on their website. IMHO, they might have a clearer statement on why they recommend rehydration.