I see it like this:  if I was a chef, I wouldn't want my customers watching as I cook.  If i'm writing a novel, I wouldn't want to be watched.  Same if I was a painter, mechanic, a cabinet maker, a landscaper, or nearly any type of artistic work.  Yes there are exceptions to this, but nobody wants to work with someone watching over their shoulder.  
 
There's a lot of other good points here, it really depends on who is asking and why, but I always urge clients to let me do my thing on my terms.

I like to do the mix myself.

Afterwards, listening sessions are cool where you make a copy of the cwp file and mess with it building it up from no fx to finished for the artists. They can give feedback about what they do and don't like.

Usually there is a ton they do like and a sliver they do not like. Learning that sliver can help close they gap between great and awesome.

As Cactus said, it all depends on who has been appointed the producer. 
In Most little studios the owner does everything. In a big studio it's rare that one person would engineer and produce. 
 

I think ProjectM hit it on the nose for me.
The other answers are exactly on as well. I feel as though there is a general conscientious here with all of your guys answers. It seems to me that not having the client in the studio during the mixing phase is crucial as there will be less distraction and less time wasted. Time is money right?
You guys brought up some excellent points referring to the delegations of job titles and responsibilities. Since I would be primarily doing all of the work myself, Producing and mixing. I feel that doing the work alone, while communicating and sending ruff mixes would be more valuable to me as the primary overseer of any material im working on for clients.
Keeping open source communication with the client during this process would save me time and allow me to gain feedback from the client to make adjusts as I need. Keeping the integrity of what the client wants but at the same time allocating my time and resources productively without any distraction.
Great answers guys!!!
and I greatly appreciate all of your advice!!
What a excellent community we have here of intelligent and talented people.
 
However, If there is any information that has not been talked about or discussed, please feel free to leave additional comments about this process and the way that you handle these type of encounters in your studio. 
 
Thanks!
-Vokalzz-  
 
 
 

Something I forgot to mention here.
If I was apart of a big studio that had different jobs and titles like "cactus" mentioned previously, then I would assume there would be a different process. Independent studios that have one, maybe two people need to allocate time a little different then split duties among staff members in bigger studios.
Something I figure I would point out since there would be a clear difference between the two type of studio operations.
 

No.
 
I don't do it anymore either. :-)
 

I only mix alone but I provide regular updates along the way to make sure i'm going to right direction.