Mosfet load control - different design compared
(note, the edits have rendered comments and previous answers not very relevant) 

The first circuit has voltage gain, but no current gain. Assuming a "load" is connected between pins 1 and 4, the load will see 0V/(almost) 5V but all the load current must be switched by the MCU port pin. When the MCU pin is low the load has 5V across it. 

The second circuit has both voltage gain and current gain. Assuming the same connections as above, the load will also see 0V/(closer to)5V and all the load current is switched by the MOSFET, the MCU port pin only sees a brief pulse. When the MCU pin is high the load has 5V across it.