There's no dearth of IM clients. It's said that if you have ten users on your network, you'll have at least fifteen different clients. Managing user's clients is like bringing order to chaos. In this regard you'll find that Openfire is biased towards its own IM client, Spark. But as it has all the features you'd expect from an IM client and runs on multiple platforms as well, one really can't complain.
So what can you control using the client control features? Here's a snapshot:
1. Don't like users transferring files? Turn it off, irrespective of the IM client.
2. Don't like users experimenting with clients? Restrict their options.
3. Don't want to manually install Spark on each and every user's desktop? Put it on the network, and send them an email with a link, along with installation and sign-in instructions.
4. Do users keep forgetting the intranet website address? Add it as a bookmark in their clients.
5. Don't let users bug you all the time asking for the always-on...