Looking at one of my VMs I see that I’ve used about 50% of my swap space. Swap space on a VM is a killer. The competition for resources like disk IO is higher on an ESXi server than a bare metal server.
Yes, it could be a huge hit, depending on how many VM’s are using their SWAP and how big the SWAP is. a SWAP is ONLY created when you DON’T RESERVE the RAM, you can never allocate more RESERVED RAM than the host physically has.