Are you talking about a bleach bypass to the negative or print?
To the negative you get highlights that go white faster, desaturation, an increase in grain, and higher contrast.
With the print you get more "crushed" blacks, desaturation, more contrast, and a little more grain.
There are also processes that will let you do parshall bleach bypass.
Generally when doing b.b. to the negative you want to underexpose about one stop, and possibly fill a little more to protect your highlights (some).
A good example of this approach is Minority Report.
A good example of b.b. to the print is Northfork, shot by David Mullen, ASC (congrats David!)
He did a partial b.b. to the print, and flashed the negative to counteract the crushed blacks.
When you are doing any lab work like this, it is absolutely critical that you test. Test your ratios, your wardrobe, your makeup, etc.
A b.b. to the negative can in fact be undone. Also, the cost of doing b.b. to the negative is less than to the print (because each print needs the additional expense). I suppose you could b.b. the interpositive, but have not tested this approach.
Kevin Zanit