If you are held back a few days by bad weather or some other unforeseen natural circumstance and you know emergency services are looking for you because you can hear the helicopters but you know you can saftely walk out on your own - would it be reasonable to activate your PLB to save them time and money looking for you even though you are safe and there is no emergency?
The PLB is very much for highlighting to the emergency services that you are in an emergency situation and need a rescue. It can incur significant costs as the services are called out but gives a fairly accurate location so the search is short.
One of your challenges here is that you may not know it is you they are looking for. Potentially the helicopters you hear could be working on something entirely unrelated.
That said, if you feel it is a reasonable likelihood that they are searching for you, perhaps because you had a checkpoint you failed to call in and you know your contact will have raised the alarm, then not activating the PLB will incur costs as they continue to search.
So activating the PLB will, in this scenario, reduce the cost and effort the emergency services need to expend - and I'd suggest that it makes sense to do this. It will also significantly improve their safety as they will not need to continue exploring - they will know where you are and can work out the most effective way to reach you.
If you are overdue, and the search party know you have a PLB, the fact that they have not received an alert from it suggests either
- you are merely delayed, and will turn up soon, or
- you are so incapacitated that you could not use the beacon (probably already dead - sorry!)
However, if you activate the PLB, the level of concern will likely increase - you've indicated that you need help, and soon. More resources may be deployed, possibly impacting any other callouts.
My recommendation is to proceed directly to habitation (without delay, but without taking unnecessary risk) and make an emergency phone or radio call (use the 112 emergency number, or the national equivalent if you're in a country that still hasn't adopted the standard; on radio, you'll want a Channel 16 "Securite" message) to ensure that the "stand down" message gets to the team who would have been activated.
Alternatively, find a big rock and drop it on your leg hard enough to break it. You can now activate your beacon with a clear conscience.
No, do not activate a PLB unless there is an emergency.
There is already a standard for signalling to a helicopter whether or not you are in need:
Source: Parks Canada Mountain Safety
If you are in need for help: raise both arms.
If you want to signal that you are not in need for help: raise one arm and lower the other.
Do not move/wave your arms.
If the helicopter is looking for you and you wave no, they can return to their base and inform your loved ones that you are OK.
If the helicopter sees you waving yes they know you are in trouble, regardless as to whether it's you they're looking for or not.