Thicker lead lets you use a soft grade, great on newsprint paper, and not snap
With a 0.9mm lead, you can use a soft grade, great for use on newsprint - e.g. for crossword puzzles and the like, and strong enough not to snap easily, as with a fine lead. Pentel is a classic manufacturer with enormous experience with this sort of product - I've been using Pentel pencils in a technical environment since about 1970 when they first appeared.
The plastic nose holding the metal lead tube may be a little fragile, although perhaps I have been careless in pressing too hard. That's the only con point I have - the design is not especially weak. I have bought several for use in different places, I'm very pleased with them,.
I had lost my 0.9 mechanical pencil, and urgently needed to replace it. It was obvious that this would fill my need and I ordered 2! I have not been disappointed.