Even with tracking, one huge exposure is usually less practical and often gives worse results than stacking shorter ones.

Key reasons:

• tracking errors add up: no mount tracks perfectly forever, so shorter exposures work better within the limits of the tracker.
• light pollution builds up too: a very long exposure collects unwanted skyglow along with your target, which can wash out the image.
• highlights can saturate: in one exposure, once a pixel clips, detail is lost. Stacking shorter frames helps preserve dynamic range.
• noise reduction: combining many frames improves signal-to-noise ratio by averaging random noise, which is especially important in low-light astrophotography.
• risk management: one long frame can be ruined by a passing light, vibration, aircraft, clouds, or other interruption. With many shorter frames, you can discard only the bad ones.
• equipment limits: many digital cameras limit bulb exposures to 30 minutes or about an hour, so extremely long single exposures may not even be possible.

Historically, very long exposures were common, especially with film. But with digital capture and modern software, stacking is usually the more flexible and reliable approach.