Some groups I am in do housecleaning like you are suggesting ... some do it as short as 4 months offline
Inactive Members

Yes, this is why I am bringing it up. It appears to me that you are in favor of it, or am I inferring incorrectly?

I am yes ... there have been a few groups I am super admin in that I have wanted to clean house but its not my group you know? But yes I support it that way you know who you have got when it comes to team matches

Is there any drawback or penalty for leaving them on?
Without even knowing the answer to that, I am one very much for organization, structure and eliminating clutter. For example, e-mail inbox at work is always empty at the end of the day...filed or deleted.
Feel the same way about non-participatory/non-active members.
What's the use? Is it really annoying that some people join a group and maybe only follow the forums and don't contribute? Is it so secret what is posted in here?
I don't see why you'd want to kick people from your group, only because they don't contribute actively. They don't bother anyone. And unless there's a rule somewhere saying that members must contribute actively to the groups they're in, this smells alot like abuse of power.
And a side issue would be what you call active. I don't play team matches, and I don't want to. I just follow these forums from time to time, but most group forums are quite dead anyway; hardly anyone contributing, few (<1) posts per day on average, etc.. Then I may stop contributing to the forums because of the few active contributors. Do you consider me inactive then?

Phobetor, we aren't discussing people who haven't contributed for x months, but people who haven't visited chess.com for x months, and that's a big difference.
Ok Kacparov, that changes things.
Still, like I said, I don't see why it's so important to "clean" the group. How does it help the group?

The number of members is true then. Many groups don't delete people because they show off how big they are, and we want to show that we aren't like them.

Should members who have not logged on in 6 months be deleted? More than 6 months? Or should members never be deleted?