Check out the Part/Assembly and all the Components
Take charge of the selected documents and start working on them exclusively.
This command is useful to set in chekout state more than one document at once
A dialog shows the state of selected documents and lets you choose which document to check out.
Some of them, in facts, could be in a state incompatible with checkout (already checkedout, released or frozen).
This entry is enabled also for generic document if the option
Revisions → Approval → 
Create structure history for all the Document types
is checked.
For further information please read the topic States and Actions in the section Revisions.