This tag offers the ability to specific a group for locking so that DTF can be smart and allow for the whole group to be locked or release the partial group so that the resources can be used by others that would be locking components at the same time. This avoids deadlocks because two tests being executed in parallel would like to lock the same 3 resources and end up failing because they locked 1-2 components each and locked the other test out.
A lockgroup should be used whenever you are locking more than 1 component and are going to be running this test concurrently with other tests. The lockgroup gives DTF the ability to correctly free up locks when they're not completely fulfilled for a testscript to execute and give those resources to another test that can execute while this testscript awaits its turn to use the available resources.