Complex sentence: Theoretically, the primary purpose of zoning is to segregate uses that are thought to be incompatible; in practice, zoning is used as a permitting system to prevent new development from harming existing residents or businesses.
Split into simpler sentences: Theoretically, the primary purpose of zoning is to segregate uses that are thought to be incompatible. However, in practice zoning is used as a permitting system to prevent new development from harming existing residents or businesses.