If you are going to use them then you need to get all 4 corners equal and that's another issue that can be very time consuming. Simpler just to leave them down. Then you only have to worry about getting all 4 feed roller corners level. Mine was out from the factory. That took that home made gauge in figure 22 and a couple hours to set it.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.