Depends on how much land you own, control with a lease, and the time available to survey and scout the land. Depends on how much available funds you have. Depends on how many deer plots you plant.
If you were a hunter using only public land, at best, you might want only one, fairly inexpensive scouting trail cam. And take the risk of having it poached.

Heck, I know one professional involved in deer hunting, who files a federal corporate tax return, and deducts the cost of all his trail cams over their useful life. He has a different basis on how many trail cams he uses. Most of the ordinary hunters can't even think of competing with him. And never will.