Some players create their own vanity guilds because they like having a guild tag over their heads. These players aren't groupers or joiners. Unreliable schedules or other circumstances keeps their WoW on single-player mode -– they like seeing all the hustle and bustle, but they aren't able to or prefer not to dive into it. Guild tags help these players feel more a part of the player population, with a "hometown" label and sense of identity that a guild provides.
Do you have any characters in a vanity guild? What was behind its creation: more bank slots, a way to indulge in a fun pun or clever concept name, a place to feel you belong? If you've had your vanity guild for a long time, have you found that it has slowly grown, accumulating friends and family members?