No, that is not the case. Using multiple threads does not magically take work away. The work to be done stays exactly the same, regardless of the number of cores or cpus being used. Multiple cores only help in terms of speed (assuming a given problem can be effectively split into separately calculable problems).

If you want to empty 20 bottles of beer and ask a friend for help you can split the "work" among you. This will half the execution time but that won't reduce the overall number of bottles to drink. If you're unlucky and you only have one 10 liter bottle instead of 20 .5 liter bottles the work cannot be split and the time required cannot be reduced.

What Kartoffel is asking for is how to reduce the overall number of beer bottles to drink. He's not keen on drinking the beer faster, he wants to drink less...