Will the chances of winning with the Harvester increase?
I can have all my hard drives with one full node server, what are the benefits of having a Harvester for me?
You chances of winning XCH is solely based on the space you have compared to the netspace.
Once you expand the amount of disks to a scale like in datacenters you can see how harvesters become essential; i.e. it enables you to scale your space better over multiple machines.
The harvester does run anyway. When running a farm on more than one machine it usually makes sense to run only the harvester on additional machines, i.e. full node, farmer and wallet only on one machine.