Harvesters works as connecting the plots into Farmer via SSL remotely. Single harvesters can contains many plots. And yes, many harvesters can connect to single Farmer, which easier for you decouple from storage depedencies.
If you confuse what is Farmer? This is what farmer looks like
This is the main software that you are running to farming your plots. Farmer must only works in single machine as your only gateway to Chia Network.
Next, what is Harvester? It’s services that running separately than Main software. Ideally, you run this service into separate machine where you store your plots.
So, imagine I have main machine that maximum 20TB capacities and running the Farmer. Also, I have another machine with 120TB plots storage and connected via LAN to the main machine.
Usually, you can share folder so main machine can access the storage. With harvester, you can avoid the hassle in giving permission and make it more secure. This are the step to do it