Since the introduction of World of Blizzard's Paid Character Transfer Service in Patch 1.12, a new concept has entered the World of Warcraft: Transfer Guilds.
What is it?
A Transfer Guild is when most or all of a guild on one server each pay $25US (or equivalent) and transfer their characters to another server (usually a less populated and therefore newer one) and re-form that guild (under the same or different name).
Why Transfer?
Many reasons have been suggested for why an entire guild would choose to pay the large amount of money to transfer multiple characters.
Faster Gameplay
The most common reason given is to play on a server with less people playing on it, and therefore having a lower latency and less lag. These players are also probably sick of waiting in queues to get into their realm because it's full! Transferring for this reason leads to faster gameplay for an entire guild.
Reliability
Some guilds formed on an older server that had persistent problems due to older, un-upgraded hardware. So, these guilds try to identify a newer hardware server in the assumption performance and reliability will be better. This reason is very similar to faster gameplay, but includes reliability. There is nothing worse than a server crash in the middle of a long 40-man raid instance run.
Bringing Friends Back Together
Many players in the World of Warcraft have created new players and leveled them up, only to discover that they have real life friends playing on a different server! Of course, now they can just transfer their characters to another realm and join them. But who's server should they transfer to? When a large group of players have this situation in common, they may decide to all transfer to a new server to eliminate this confusion. A transfer guild is formed.
To be the new "Top Dogs"
Another reason (that few guilds will admit to) is for a lower ranked guild (in regards to Raid progression) to become the TOP-ranked guild on a newer server. This guild will have weapons and armor that no one has even heard of on these servers. This can make a guild feel very good. For this reason alone, many players in WoW look down upon transfer guilds because they feel like they are being given unearned respect.
To Be Forgotten
For whatever reason, a guild may have achieved a bad reputation on their realm. By transferring their guild, they have a chance to start fresh and either change their ways and be liked, or act in the same way. The character transfer service gives them a chance to start over.