The operation of your network printers has no dependency on the mail server whatsoever.
Print spooling for networked printers either happens in the local workstation (in the case of a stand-alone network printer) or in the local file/print server where the printer is configured.
If your networked printers and print queues were somehow defined on the remote mail server, they would not work properly at all, since the heavy volume of print traffic would have to traverse the WAN link twice....both from the local workstation to the server and then back from the print server to the print device..... the disk utilization would be the least of your worries as the network would be slow and unreliable at best.