A daily log is the field's official diary: who was on site (which subs, how many workers), the weather, what work was performed, deliveries received, inspections, and any problems or delays. It's usually kept by the superintendent, one entry per day.
Daily logs seem tedious until you need them. When a delay claim, a differing-site-condition dispute, or a weather-day question comes up months later, the contemporaneous daily log is the evidence that settles it. It's both a management tool and a legal record.