ADDITION: I think to level set the answers the OP needs to describe the level in the WBS or schedule about what he was thinking when asking this question. I am inferring from many of the answers provided here that many are describing a situation where a competent and experience technologist is asking the PM permission to do the next task every 15 minutes of 1/2 hour. I described in my answer below a situation of controlling work packages, wherein you can have hundreds of activities and tasks and can span a duration of days, months, or even years on really complex projects.
Part of cost and schedule control is this concept of the Work Authorization Document (WAD). This document, delivered to the team and / or individual resource, is the control order that describes what work is being performed, by whom, when, and where, the target cost and time, and the method of tracking their work hours, e.g., charge code(s).
The WAD can contain a single work package or several, depending on the nature of the work, dependencies, and risks. The team or individual is authorized to perform the work issued in the WAD and nothing else.
Carte blanche approval to just allow work to go without these types of controls means your project is out of control. Work and materiel need to be coordinated, risks and issues need to be worked through, cost and schedule variances need to be mitigated, change requests need to be assessed and scheduled, and scope needs to be verified and validated. Too much else goes on within a project for a shotgun release to be effective.