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Beyond avoiding saturated stars and overwhelming skyglow (shorter subs = better) versus minimising the relative contribution of read noise (longer subs = better), an advantage of many subs is that it improves the ability of stacking routines, such as sigma clip or median, to remove artifacts. More, shorter subs, also means that you can toss out those that were affected by tracking errors, wind etc.
As Rick noted, if we had near-zero read-noise cameras (and a powerful computer for processing), then in theory, we should be taking 3600 x 1 second subs for every hour of integration. But until that happy day, we're left with a trade off.
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