[rch]

The article mentions that it has stopped a few times, which would affect accuracy.

The Clock of the Long Now operates on similar principles (temperature difference), but separates timekeeping from the display mechanisms in part to maintain accuracy.

[logfromblammo]

And also so that the power required for the display may be redirected to the more critical timekeeping function if necessary. If you only have enough power left to keep time for the next month or to power the display for the next day, you turn the display off and hope that more power is added to the system during that month.

[rch]

Yes exactly. The other reason is to build in the notion of human interaction.