If not used, P2 pins are internally pulled up by pullup resistors and so, the state of those pins is defined (all are high level). P0 pins have no internal pullups, so they are floating. It is a good idea to initialize them at startup to 0 (MOV P0,#0), so there is no need to hardwire them to ground or Vcc. If initialized to 0, they are internally pulled low by transistor and are not floating anymore.