I've never really had a policy on friending and defriending; it didn't seem necessary because the majority of my posts were fannish in nature. If people friended me, I automatically friended them back, and if they defriended me, hey, that was ok too. I never took those things personally, and I still don't. Truthfully I was never really active on LJ until 2007, though I've had an account since 2003.
Now I post almost every day, and an increasing number of my posts have personal content. Writing helps me process my life, and I'm finding it keeps me healthy. For me it's too much of a headache to have one journal for fic, a separate one for personal ramblings, and one for music posts, etc. etc. Those things are all a part of who I am, and it's easier for me to just have them in one place rather than make some kind of artificial distinction.
All of which leads to this: there are a couple people I friended after they friended me, but we've had literally zero interaction. I don't keep track of how many comments a given person has left me. Life is short and busy, and I know there are many other things that rank higher in priority than commenting in peoples' LJs. That said, I do have a general sense of the people I interact with here. If we've never interacted and I'm aware of that, I'm going to defriend you. Maybe you're just here for fic, which is fine. I don't plan to lock my fic posts. Some people like to read anonymously--for whatever reason--and that is ok. You won't be missing much by not having access to my f-locked personal posts. You're probably not even interested in them. :) If I defriend you, and you'd like me to add you back for some reason, comment here, email me, or message me.
Also, going forward, if you friend me and then never comment or say hello, I most probably won't friend you back. This is not supposed to be some big, dramatic thing. I'm simply no longer comfortable having certain posts viewable by people who are essentially invisible to me. And yes, I know that privacy is an illusion when it comes to the 'net.
One last thing and then I'm done. I promise. *g* You don't need to ask my permission to friend me. However, I don't always notice when someone's added me, so if you want me to add you back, please comment or message me in some fashion. I promise you I'm generally easygoing and approachable. I enjoy the interactivity of LiveJournal; that's why I'm here.
ETA: I swear I'm not a drama queen. Actually, I generally hate being the center of attention and much prefer to observe. :)