I agree with raskae that bokeh seems got nothing to do with mf.it's the f number and the background distance that decide the background blur.i use mf only when it's at nite where light aren't enough to let the camera detect the focus.and when we are shooting macro.sometimes when red dot flicks,sometimes the focus is not achieved.that's y we have to fine tune it the focus ring if your lens has FTM like mine.
And i use MF when i'm shooting with tripod where i wanna get myself included.i compose the focus and setting,when the setting and focus is achieved,i'll turn it MF.so the next shot,the focus is still the same.
Y bother use MF if AF does better job to our picture.except you want to compose a all blurred picture for some artistic reason.
I use af all the time.