Obviously, the moral behind this thread is, "it depends."
You have the hardcore rightwing who are telling you that they will [insert illegal activity here] your [insert close family member or friend here] if you even so much as mention grass, and then the naturalists who are telling you to... erm... "spam level 100 bidoofs."
I think that anything can be pulled off, it's just a matter of how.
So my two cents are, without ruining the creative process by making a long, comprehensive list:
-Abandoned town-like areas that aren't in this sense a town: Almost mandatory.
-Well established cities: Not even if you need it for a plot element.
-Natural based towns: Yes, but...
1) Grass just needs Pokémon data. It's irritating and confusing to walk in "empty" tall grass. So, don't add rares, and keep the encounter rate LOW.
2) Because it needs Pokémon data, NEVER make this one of the first towns.
-Inaccessible grass? No. If you want to fence off some grass in a city, make it possible to get there somehow. Think of all the lame fences in RSE - leave the town and loop around the fence. Grass should never ONLY be present as a decorative feature. However, if there is already accessible grass, then it's ok to have some inaccessible decorative grass.
[/long, comprehensive list]
There is my opinion. Now go and study.
-Lyzák