I think you mean the SFP slots..., on both these switches the last few ethernet ports are linked together to an SFP slot. So if you use an SFP slot you loose an ethernet port.
The SFP slot gives you a choice of GBIC connectors depending on available fiber (single, multi-mode), distance, or even copper. etc Obviously you allready have a copper link through an ethernet port so that won't help much. If you need to go long distance (> 150m) you should consider glass fibers and thus might need GBIC's for glass to replace your copper cables.
As the switches can do both MDI & MDI-X you dont' even need a cross cable.
