ignoring auto MDI/MDI-X ports the correct usages would be any 'end' device such as a pc, router, modem and printer require a crossover cable to connect to each other. A straight through cable is used when connecting one of the above to a switch. Although switch to switch connections use crossover cables also. so..
Pc/router/modem/printer -> Pc/router/modem/printer = crossover
switch -> switch = crossover
Pc/router/modem/printer -> switch = straight through