Genghis
My company mandates monitoring guard in case of loss of comms. As the previous posts added this will be the frequency ATC will try to call you on when you go lost comms because they forgot to hand you over. On many frequencies around Europe, you wouldn't believe how quiet the frequencies can get, so you wouldn't even necessarily realise you have lost comms until you're out of range.
In the last few weeks I have also heard a pilot from my company provide assistance and give a relay to an out of comms RYR who hadn't been handed off in Spain, I have also heard a pilot providing assistance on guard to a light aircraft putting out a PAN, and providing a relay.
Guards purpose, and the monitoring of guard is imho an important part of the safety net.