You only need to enable the MESH functionality if one or more of your APs are not connected to the main LAN. E.g. An AP in a room or part of your building that is not possible to run structured cabling to.
Yes, exactly! You have absolutely no need for Mesh functionality in that instance and even if you do enable it, Ruckus SmartMesh is inteliigent enough not to create a mesh infrastructure because it knows it could reduce overall performance.