From a physiological perspective, I can tell you that holding the breath for a few moments in the middle of an extremely intense action that involves stabilizing the torso is virtually a necessity. When lifters execute circa-maximal power or strength lifts, they always hold the breath, and use the 'valsalva manouver'. This basically consists of trapping air in the lungs and pressing down with the diapragm, which increases intra-abdominal pressure and stabilizes the lower torso/spine. This is a relatively 'instinctual' reaction that really helps when doing something extremely strenuous.
In theory, nage probably shouldn't need to use that much force in a throw, but occasionally, it might be a good thing. We probably use it fairly often, for a moment, when we hit the mat during a hard fall. Although sometimes it's good to deflate as you hit, sometimes you need to momentarily tense up, valsalva and all, in order to protect yourself.