edy4eva is right about the hotels and the times/layovers...

BUT: if you booked a flight that is more convenient to you and the layover is therefore longer (i.e. 8hours) than the original itinerary (i.e. 4hours) proposed by ek, than they will give you nothing.
had that once, when I travelled from germany to oman and didn't want to do the overnight flight and chose the daylight flight into dxb. then they did not give me the voucher.

however, since i am ek gold they did it in the end as a courtesy...