Inactive means that particular contact record won't show up in future searches (unless you choose to show inactive items), making it easier not to see unwanted records. You wouldn't want to just delete the item, as that would remove it from the job record altogether, and that is prevented if the contact is still in use by being attached to a job. If you wanted to actually delete, you'd need to edit the job, remove it from the job(s) where used, and then it could be deleted. But most likely you want to keep a record of that contact for past jobs, so inactive is a better option for a contact you no longer need at all (perhaps they retired or something)
However another option if they are the same person and still a valid contact you want to search for and use for future jobs, is to just merge your duplicates together instead. That way all your jobs for that person are then attached to the single merged agent record, and you no longer have duplicates. This may also make management or sales reports more accurate, as well as locating all jobs attached to a particular contact much easier when searching in the main Contacts view on the opening screen.
In regard to merging duplicates, as copied from the What's New info document:
"To do so, use the main screen Contacts View to display the desired contacts. Verify your
master contact is up to date with all desired details. Then select the master contact containing the most recent and correct information first, followed by other duplicates for that contact while holding CTRL. If the Merge Contacts button that appears at the bottom is used, information in the master contact will apply to all jobs where all selected contacts were used and the other duplicates permanently deleted. Similarily Companies associated
with various contacts may be merged together to eliminate duplicates from the Maintain > Companies area."
(similar info in help topic under Contacts - Maintain Contacts link).
In your case it sounds like merging them is probably what you really want to do. Unless they are old retired agents, and you just want to remove them from your sight when searching- then inactive could be the way to go.