Benefits
As mentioned earlier, both Trillian and Gaim have their own advantages. For example, Trillian automatically logs all messages to a text file on your hard drive so you can later reference the text logs if you need to. Trillian also offers the capability to search the Web and Wikipedia (an online encyclopedia), to do such things as pull definitions from the Web while chatting.
Gaim can run on non-Windows platforms, which for the Linux or Mac user is quite appealing. Gaim also bring users what are known as "Buddy pounces," which, in essence, is a macro that can be played when an IM event occurs. For example, you can set your IM client to automatically send an IM buddy a specific message when that person logs in.
Unfortunately, although with Trillian and Gaim you gain the benefits of being able to use one IM client with many IM services, you might lose some offerings from the individual IM clients themselves. Most of the basics, such as file transfer, are there. But some IM services have specific offerings, such as IMVironments and Audibles in Yahoo! Messenger, that are unavailable through Trillian and Gain. Depending on your affinity for such IM client–specific offerings, you might want to think twice before you uninstall your IM clients and use only Trillian or Gain. Fortunately, nothing is stopping you from having Trillian and Gain installed concurrently with your other IM clients on your machine. Of course, only one IM client can be logged into a given account at one time.
The bottom line: Trillian and Gaim both can act as a single front end for instant messaging with your various IM accounts. Both alleviate the need to run multiple chat clients on your workstation in order to interact with IM buddies who are spread across the spectrum of IM services. Of course, it is always a good idea to give both Trillian and Gaim a try, to see which program consolidates your instant-messaging needs best.