When do pilots actually use ‘wilco’? I know it means “I have understood the instruction and will comply.” However, any instruction that


is a clearance,
concerns runway use or
contains altitude/level, heading, speed or squawk code


should be read back. And that seems to cover most instructions.

So what is an instruction, but does not require a read-back and may be instead answered by just ‘wilco’ (+ callsign)?
When instructed to report something.

ATC: Cimber 626 turn left heading 120, cleared ILS approach runway 09, report established
Pilot: Heading left 120, cleared ILS approach runway 09, WILCO, Cimber 626



ATC: OYABC airborne time 33, report passing Dalhem
Pilot; (Roger), WILCO, OYABC



ATC: Lufthansa 135, traffic is a Boeing 737 on 5 miles final for runway 09, report in sight
Pilot: WILCO, Lufthansa 135