How is locking a sequence different from deleting a sequence?
Locking sequences is not the same as deleting a sequence. Deleting a sequence is a permanent, non-reversible action. Locking sequences removes the sequence from your view, and can be accessed again.
If the sequence is enabled when it's locked (the master toggle switch to the left of the sequence name on the over view page will be green), prospects will continue through the sequence steps. If disabled, the prospects will not continue through the sequence.