Not necessary, but makes things a lot easier.
With wood, you can work with a substructure that basically adapts to the terrain. For example, I have about 40 cm difference in height between the indoor floor and the outside terrain. I don’t want steps going from inside to the terrace, so I build the substructure in such a way that the terrace boards end up approximately at indoor floor level. This is a bit more complicated and expensive in terrace construction, but then I can save myself special sealing measures because the ground outside is basically at floor slab level. For me, a splash protection strip and possibly a dimpled membrane on the facade are enough.
But that also has to do with my soil, which drains quite well. So the risk of standing water is not very high for me.
If you wanted a stone terrace, the corresponding substructure would have to be set much higher. So then you would have at least soil (or the substructure) directly next to the house along the length of the terrace. Here, more measures have to be taken to protect the plaster and masonry from standing water. Also, the risk that heavy rainwater pushes directly against the window is much higher because it can nicely flow in at the same level over the terrace.
You would then need the gutter or even drainage. The sealing of the window element to the outside also has to be done much more extensively. With my variant, basically the minimal requirement of driving rain tightness is enough.
Although I still want to seal it with liquid plastic. Mutterkiste and Vorsichtsporzellan and all that.