Which Radios to Switch On?

[fireflybob]

Do you teach your students to only switch on the radios they require and/or know how to use or do you require them to turn on ALL the radios for all flights?

For example, for a circuit detail do you teach them to turn the DME and ADF, as well as COM and TXPDR?

Can you list any reasons supporting your views please.

Finally, does switching, for example, the DME on and off on every flight significantly effect time before failure?

Thanks.