It depends on the setting. For example, where I worked at as aide in LTC the nurse had 28 residents on a given unit. Writing a not of every resident every shift was impossible. If the resident had something happen outside their norm (i.e. fall, increased confusion, fever, etc.) the nurse would write a note on that and include his/her intervention for that and chart on the outcome of that intervention.
In acute care, the policy also varies from place to place. At my first job, complete head to toe assessments had to be done (and charted) q12 hours. If, in between those assessments, there was a change in condition the nurse had to chart on that change. Most nurses did their assessments at the beginning of their shift and then wrote a note toward the end of their 12 hour shift just to summarize the condition of their patient and that their assessment was unchanged (if indeed it was).
On the telemetry floor, we had to chart a head to toe assessment every shift...sometimes they were 12 hr shift, sometimes 8 hour shift. So, some patients would have 3 assessments charted per day, others only 2. Again, notes as needed. At the same hospital, on med surg floors, where each nurse had more patients, only a focused assessment had to be done each shift. ICU nurses would have to do a head to toe assessment much more frequently.