At some point in time, network switches are full, and the network needs to be expanded with more switches. These switches can be connected together via regular ethernet cable. Sometimes it is desirable to use the SFP or SFP+ ports.
SFP and SFP+ ports are switch ports in which one can still choose which media one is going to use. Different media types are for instance copper wire, or fiber optic cable. The difference between SFP and SFP+ is that SFP can be used for speeds up to 1Gbps while the SFP+ can go to 10Gbps. SFP+ is downwards compatible, which means that they can communicate with SFP ports, but only at the 1Gbps speed.
When we connect 2 switches together, we try to use more than 1 port for the connection. We use link aggregation, which bonds the ports together. For example when using 2 ports at the same time, we get speeds of 2 Gbps instead of only 1Gbps. This makes switch to switch communication a bit better.
When switches are a long distance apart (i.e. different building), the usage of fiber optic cable is preferred. This has to do with the fact that there is no electric current involved in the transportation of the data in the cable. The SFP module uses a laser to send light waves thru the cable to the other SFP module. When using copper between different building, one always has to make sure that the earthing or grounding is done correctly (potential equalization). It can cause a lot of issues which are very difficult to trace when that is not done. Fiber optic cables prevent those issues entirely.