When would a pilot request a "VMC descent" or "VMC climb"? Can anybody explain what's the point of this and in what kind of situations a pilot needs it?
ICAO Doc 9432 &quot;Manual of Radiotelephony&quot;

8.3.3 An aircraft may request a clearance to climb or descend maintaining own separation while in VMC, in daylight, below 10 000 feet in airspace classes D and E. The clearance shall include information on essential traffic.
Example:
P: FASTAIR 345, REQUEST VMC DESCENT TO FL 60
C: FASTAIR 345, DESCEND TO FL 60, MAINTAIN OWN SEPARATION AND VMC FROM FL 90 TO FL 70, TRAFFIC WESTBOUND FRIENDSHIP FL 80, ESTIMATING WICKEN VOR AT 07.
It would be needed when otherwise the flight path would not be cleared because ATC cannot ensure separation with the conflicting traffic. The pilot agreeing to maintain their own separation in VMC allows the level change to be cleared despite the conflicting traffic.