The problem is that you really don't want to switch to HDD or SSD, because that will never go right. The only reason why you would still want to swap is that some memory is actually not used by applications. Basically: if you really run out of memory that is required for calculations then everything grinds to a halt: you either get disk trashing or you simply get an error. Compare that with a lack of CPU power: everything goes slower, but that scales more or less linearly (more or less since current processors do not allow you to boost indefinitely with normal cooling). So yes, you do want to make sure everything fits into memory and leave some spare memory for disk caching and the like.
Biting the hand that feeds IT
