I keep them.  I have a lot of lurkers or people who come back after awhile and start posting. 🙂

I used to purge them after 90 days for a few reasons:

• to prevent spambots from using these accounts later. 
• to stop people from having duplicate accounts (since people would make an account, leave for like a half year, come back and forget they had an account already and make a new one).
• to stop people from sitting on desired names (used to be a lot more common than it is now, but people used to register on sites they had no intention of being active at just so they could deny others using that name).
• to kind of encourage people to be part of the community instead of just joining and fading away. (I really don't think it worked though.)

These days I don't care as much. They aren't taking up enough space to matter in the database. Plus in the past I have had people who were gone for long periods suddenly return.  I kind of doubt those with no posts, and thus no connection to the community, will suddenly decide to return. (And if they did they'd probably just end up making a new account anyway. ) But it doesn't hurt for the accounts to be left alone so I'm not going to mess with them.

I mean..there's no hurt in keeping them, right? Some of them eventually come back, just like zoldos said.

I'm doing my second clean out pretty soon, the reason? It does take up available usernames that people may want to use. So that is one good reason.

I tend to keep members myself too as mentioned above you may get them coming online to view and maybe post eventually, i did have in the past a 3 year rule but noticed from this 1 in 5 members normally came back and tried to sign in after this period of time so now i keep members unless they spam or have been given too many warnings.

For me personally, I'd keep members like that. If at least for the vanity metrics like member count lol because why the hell not? As long as my member list isn't full of spambots then I'm happy enough. From a user perspective, as has been mentioned, some of them may have signed up to have a lurk and you'll never know when they are thinking of popping back into the fold. I'd rather make it easier for them than harder.

Even I never delete accounts based on inactivity. You never know what makes them interested and they come back and become super active. As far usernames are concerned, there is no dearth of usernames and avatars if someone is interested to join a site.

There is batch update users built in XenForo that helps eliminate those with 0 post count. I personally wouldn't do that because they don't take up significant space, in fact, barely.

My website with almost 40k members, most of them have 0 post count, however they almost all buy products on the marketplace so I always keep 0 post count users as they're either there to lurk, or buy stuff which is always a plus.

Posted by: VirusZero

• to prevent spambots from using these accounts later.

How can a spam bot use a 0 post account?  It would need the password.

Posted by: suny

Even I never delete accounts based on inactivity. You never know what makes them interested and they come back and become super active. As far usernames are concerned, there is no dearth of usernames and avatars if someone is interested to join a site.

I operate similarly. However if, after a year of being a member and they still don't post, that's when I debate on deleting the account for inactivity. Happens very rarely though 

Sometimes the odd spambot does manage to get through all the various anti-spam protections a site offers and can register. These spam accounts don't always activate right away, sometimes they sit dormant until enough accounts have been created across various sites for the bot to start dropping spam with. Plus sometimes sites employ a time based post restriction (like your account must be <age> before you can post or have a signature) and waiting means these restrictions will be gone when the bot actually intends to spam.

Other times people will manually create accounts for bots to use later on.  They created the account and then can just enter it into the spambot script so it knows exactly how to log in. In this case the spammer just has to register and walk away, the bot will come back later to do the actual job.

I delete the following accounts automatically via cron jobs:

• Users with 0 posts after 365 days of inactivity
• Users with 0 posts and have been banned (spambots)
• Users who have been rejected from registering via moderation (spambots)
• Users who have not confirmed their email address after 365 days from registration

I don't really see the point in keeping them.. They add no value.

I just checked the forum site  I moderate has 11348 members but only 9-10 are active at any given point of time. And some members have 1 post or even 0 posts but they are all there. Only the accounts of spammers deducted and they do not count in the members list.