Unless the tank will house aggressive carnivors where inverts will not be permitted, the mech filtration will not be needed at all. With a LR
tank reef or otherwise, the fauna withing the system become your mechanical filtration so to speak.
All mechanical filtration does is filter out/collect large particulate matter from the water. As I said though, if you leave the HOB
running without a filter insert it can easily be placed back when needed. If used 24/7, mechanical filtration can often become a hinderance to water quality.