Both my birdbox systems and my Portable (garden) PiCam need to know the time & date in order to properly time-stamp video clips and events.
Up until now I have relied upon an old HP Compaq D510 to help set the correct time, but I've finally got around to replacing this with a not quite so old Pi B v1 Rev1.
Although the D510 was quite economical, my Pi replacement should consume less than 5% of the power of its predecessor.