Do you delete inactive members on your forum to keep the member list short and 'cleaner' or do you not care about having lots of accounts registered? I personally don't mind if people register and never come back or don't even log in once.
If people have registered then they clearly wanted to join and may at some point in time come back to the forum. I tend to leave accounts unless they are clearly spammers or people trying to cause trouble. It lets people come back to the forum whenever they like if they feel like it.
I would only delete an account if it was a spammer or someone asked for their account to be deleted for a valid reason. If someone signs up and then never logs in I wouldn't really care as it doesn't really affect the forum at all. Deleting accounts should really only be a last resort if you need to. You wouldn't want to worry people thinking their account my disappear!
I like to give people freedom to do what they want, assuming they are not being rude or posting stuff that is off topic. Well, people, generally speaking, are doing you a favor by being on your forum. It's like customers to a business.
When it comes to deleting accounts I never deleted inactive accounts whether they are banned or just inactive. I keep them for two reasons. The first reason is that you never know when someone may come back to the forum who has an account after being away for a while due to real life getting a little hectic and two, it helps with finding out if members are ban evading who have been banned. I never ban easily and if you get banned on a forum I run it is a genuine reason and I do not tolerate ban evasions if you have been banned.
I don't see a big deal with deleting inactive accounts. In some cases, they maybe inactive as a result of one reason or another and will definitely come around when they feel the time is right.
I used to delete inactive accounts when I first started. But I’d first email them to give them a chance. Now, I keep all accounts with the exception of banned ones. I figure they took the time to register, who am I to tell them when & how often they have to come back on!