The Dell PowerEdge 1950 has eight memory slots. Previously, it had 4 x 2GB in there. We need a bit more memory so added an extra 2 x 2GB. On boot, the BIOS warned us that the preferred configuration is to fill all 4 additional slots but allowed the system to boot.
I'm aware of the requirement for pairs of memory but what have we "lost" by leaving it potentially unbalanced like this?