As an ATCO I must admit one of my pet hates is strobes on during ground ops. They do dazzle, they are annoying, and they're not achieving anything really apart from blinding people. If you don't believe me then sit in the tower and have an Airbus taxy past with them on because his ops manual says so (soon got that changed) - it ruins your day (and your night vision).
As for types like some PA28's where it's all on the one switch - daytime you can see the aircraft, night time the nav lights should be sufficient to people that the aircraft is active. If anything the strobes actually stop you seeing that the prop is on because of the dazzle effect.
As others have said - just before you enter the runway, not before. When you vacate the runway, not after.