Putting a preamp on a integrated?

I do not plan on doing this at all. But I heard some people do do this and was wondering if there are any advantages to this. I am VERY happy with my Mcintosh MA6900. Just thought I'd ask. I'm still very new to this. Just trying to learn. Thanks to all of you. I really appreciate your kindness!
Ed

The MA6900 has pre-outs AND amp-in so that the preamp and amp can both be independant. This is a rare feature in integrateds (pre-out is somewhat common but amp-in is definately rare) but allows lots of flexibility if it is ever desired. Some people may want to use an HT processor/preamp as the preamp stage and use the 6900 to power the front speakers, etc. Glad you love your 6900 - it is a very fine sounding piece and I would like to have one too! Take care - Arthur

Thank you Arthur! I didn't know that you could connect a processor/preamp for HT. That's why I ask these questions. You learn as you go. Thanks again for all of your help!
Ed