Difference between *271 (timegroup override) and *280 (day-night toggle)

Could someone enlighten me as to what conditions would commonly suggest using a time group override instead of the day-night toggle feature?

I am afraid that I have these two items completely confused but it appears to me that a time group override is ‘sticky’ in that it must be manually reset; while that the day-night toggle lasts only until the next time condition is met. Is that right?