the AMM will stipulate at the beginning of the task, open cowls IAW.... and at the end of the task it would be something like close cowls iaw AMM....
That will work if there is only one task being conducted inside the cowl. Once they are opened, its possible that several maintenance items will be taken care of. Each MM procedure will have an 'open cowl' and 'close cowl' step. But if you've finished your work and there is another task or two under way, you'll be leaving the cowl open. Whoever is finishing up the last task may not have been the person who opened the cowl in the first place. And they might not know whether anyone else is still working in that area.
So, log books (or other records) need to be used to track all out of configuration changes. And there needs to be a process wherein all such changes are accounted for before the aircraft is released from maintenance.