It's simple. Some people might say it's stupid. However, it works, and most people have NOT thought of it (until now.)
This lets you help your guild members into giving each other items without having to leave their location, for instance one member is in Booty Bay, and another is in Silvermoon City.
There are many different things you can do to alter this method, but I will be going over the one I think is best in most situations:
Once you have created your guild, (or if you already own one,) buy a new bank tab and name it Trade Purposes or something similar. Make a rank named Trade Purposes or something similar that has permission to access 1000 items in the Trade Purposes tab per day. Then, if two guildies need to give each other items, you promote/demote them to that rank, they deposit their item(s) into the Trade Purposes tab, and then they remove the opposite persons gold or item, and at the point, you demote/promote them back to their original rank.
You can use this for more than trading. Say they need a gem cut? Done. A transmutation? Presto. Anywhere that someone has access to a guild bank, they can trade or make something using their profession for another guild member.
Last but not least, if you think this sucks, it would be better off if you didn't reply...