[rikur_]

I was taught that when I'd got nothing better to do with it, to use box 2 to listen out on 121.5.
On a cross country flight I typically use box 2 for ATIS, quickly talking to airfields I'm passing close to or listening out on the next frequency - but on a local bimble I'll generally have it on 121.5.
A few weeks ago I listened to a light aircraft mayday situation on box 2 - all successfully handled by D&D and others - but on reflection whilst I learnt a few things from it - I found it very distracting.
Given the good levels of ground based coverage in the UK, and I believe most airliners are listening out on 121.5 (??), then is there really any point in a GA bimbler doing so?
In theory there could be an aircraft in distress below the level of ground based coverage - but in which case lots of airliners should hear this from 35,000ft?

[2Donkeys]

I don't think it's bad practice at all to listen out on 121.5. As you say, in the UK, coverage is good and the frequency is well monitored so the actual likelihood of you being required to relay messages is quite slim.

On the other hand, you may be the one with the emergency one day, and so the true value in having 121.5 selected on box two is that it might save your skin by leaving you one less thing to do.

[Iceman]

For those with Garmin / Avidyne IFR GPS units, e.g., 430' 530, 650, 750, 440, 540, remember that 121.5 MHz is one button selection away if needed quickly and not already selected - just press and hold the frequency toggle button.

I always fly with 121.5 on box 2 so that I can monitor it at all times and so that it's available immediately.

Iceman

[Paultheparaglider]

Just remember if you hear anyone call out on 121.5 the first thing you have to do if you want to sound professional is to interrupt in an angry voice and say "You're on Guard."

I learnt that on PPRuNe.

[JonathanB]

And if you miss a call or need a something repeating on your current frequency then you can say "Sorry, crossed with guard"