Benefits of upgrading client version?

[xeon]

Hi,
I'm wondering what benefits would give me changing the client version I'm using.
Given as assumption that new clients have bugfix/stability improvement, what you have to consider when doing this evaluation?
For example, what about
- clients changes between "major" release? My mul files for example are currently a heavy modded version of Age of Shadows files. I can simply put the new client version in UO client folder and run it? What about incompatibilities?
- what about encryption? for example, I'm trying to login with a 400c riced client and I login successfully, but already starting with 400l I can't login. Pol is obviously configured for no encryption.
- anything else?

By the way, when you change the client release, have you also to change your mul files?

[Yukiko]

My mul files for example are currently a heavy modded version of Age of Shadows files. I can simply put the new client version in UO client folder and run it? What about incompatibilities?

I can answer this one. I have had problems when using UOML art, gump and tiledata muls with the latest version of POL (0.99 development releases) and newer clients. The problem I have with POL 0.99 is it doesn't create a valid tiles.cfg file and thus POL will not start. The client issue I have is the index files for the various MULs are different and sometimes I get erroneous issues when using newer clients with my modified UO:Mondain's Legacy files.