In addition to the many reasons already mentioned, some school labs use them because bench meters are less likely to escape the lab inside a student's backpack. The large size is a positive attribute, making the meter more likely to remain on the bench. I think that's one reason why some low-end bench meters are made with precision and accuracy that is unremarkable compared to similarly-priced handheld meters. For a home lab, or any reasonably secure workplace lab, this shouldn't be a factor, though.
I think for most individuals, the best bang for the buck is in handheld meters, usually. But if you need to leave the meter on for extended periods of time without worrying about battery life, or if you find yourself needing precision and accuracy unavailable in a handheld unit, go for a bench unit.
Or if you really will be using it always on the bench, I think a bench unit is a bit more convenient. It's just that it's a lot more convenient to use a handheld meter on the bench than it is to use a bench meter in the field.