I'm finishing a small PCB that has too many traces in order to realize a good ground plane. The circuit doesn't need particular layout precautions, so this is not a problem.
Since the ground plane option is excluded, is it better to leave an unconnected copper pour or remove all the unused copper?
I will have the PCB manufactured, so I have no etching problems.
You can stitch otherwise floating island copper to the ground with short traces and vias.
General advice is usually to avoid floating copper islands, especially near RF circuits, because of sneak coupling and other unforeseen effects.
When doing polygon pours, we normally use the "Remove Dead Copper" option in Altium Designer.
Sometimes commercial PCB manufacturers will request to put down floating copper to prevent "copper thieving" (to balance the electroplating). See, for example, this question. A review of the possible effects should be done before agreement is granted.
For EMC compatibility it is better to remove unconnected copper, because at high frequencies it can pick up noise and act like a resonator, and cause excessive radiation.
