A good practice is to allocate enough swap space to support a failing CPU or system board during dynamic reconfiguration. Otherwise, a CPU or system board failure might result in your host or domain rebooting with less memory.
Without having this additional swap space available, one or more of your applications might fail to start due to insufficient memory. This problem would require manual intervention either to add additional swap space or to reconfigure the memory usage of these applications.
If you have allocated additional swap space to handle a potential loss of memory on reboot, all of your intensive applications might start as usual. This means the system will be available to the users, perhaps possibly slower due to some additional swapping.
For more information, see your hardware dynamic reconfiguration guide.