VMs in general use more CPU power as you have two OSes each doing things like updating their real time clock... There are VM aware OSes that will not do this, but it needs special code and CPU support which means you are often lagging behind the latest (to be fair this is rarely important) A container will normally be slightly faster than a VM never slower (assuming a reasonable OS - I can write an exception if I was malicious) and so there is a lot of interest if they are good enough.