Very few cases of that. It's by chance, but many of the bushes used to place wards in give good vision on paths you want control over.
But yeah, not every bush works (for example, I still don't get why anyone on TT would ward the top bush, as chrono's map told me. There is no vision on any point or path except for the place it stands, there is no direct threat from there that you couldn't cover with a ward which at the same time covers something useful too)