John Shriver , Jan 26, 2009; 10:43 p.m.
The primary advantage of push processing is that you can get somewhat finer grain than the faster film developed normally.
Otherwise, your "advantages" of push processing can also be achieved in printing. Want to lose shadow detail? Increase the paper contrast, and let the shadows burn black. Making a straight literal print of a negative is missing much of the power and flexibility of B&W printing: contrast, exposure, burn, dodge, etc.
Of course, the other way to look at pushing is as a Zone System approach. If you only want to record a narrow scene brightness range, you under-expose and over-develop.
But, if you're not working in a Zone System way, the advantage of the faster film is that you have more exposure latitude, so your exposure is less critical. Can be really helpful in a night club.
Of course, the fast films all cost more than the ISO 400 films -- that can be a perfectly justifiable reason for push processing.