Lets say you have 5 models. You don't want to invest a bunch of money to convert all of them to 2.4 at the same time. With a module radio, you can only convert them as you want to, and still only need one radio at the field. just pop the correct module in to fly the plane of choice.

Lets say you have a modle with retracts, smoke, flaps, doors on a seperat channel, and all other controls. From my counting that is 8 channels needed, an module 9303 would do the trick.

I am sure there are many other reasons, but for some the decision to just get a DX-7 is not easy.

I have just about decided to get a 6M instead of 2.4. There are only 2 other fliers at my field on 6M, so there are plenty of channels available and I really don't need to worry about interferance or how a new technology will work.