What are "Junk" miles and are they good or bad?

When you are training for an event and need to log long miles are there any miles that you run that are "junk" miles? Meaning are these just miles that you are logging to reach a specific distance or certain amount of time? Or are they miles you are running with a friend or group that aren't being done at your specific training pace?

If it is the former and you are not logging these miles at the necessary training pace then yes, they are junk miles and aren't providing the specific benefit you need for your goal.

If it is the latter and you are doing a social workout with friends then no, these are not junk miles but are miles that are being logged in your "mental" area of training. Everyone needs a break from time to time to recharge and nothing works better than spending some time with friends.