Drone knowledge

Do I need to keep a flight log?

There is no obligation in the open category. You may fly without writing anything down.

The situation is different in the specific category: There, recording flights is generally a requirement of the operational authorisation or part of the operations manual. Your authorisation specifies exactly what must be documented.

Why it is still worthwhile

A flight log is particularly valuable when something goes wrong – and that is rarely the moment when you still remember the details:

In the event of damage, it proves the conditions under which you were flying. If damage is attributed to you weeks later, the entry is your best evidence.
When reporting an occurrence, you need the time, location, weather and parties involved anyway.
For maintenance, operating hours per device and battery cycles are the basis for sensible maintenance intervals.
In dealings with clients, a properly documented operation is a mark of quality – some industrial customers now require it.

What it should contain

Date and time, location, device used, remote pilot, purpose of the flight, flight duration, weather, special circumstances and occurrences. That is sufficient. A table is enough; many fleet systems automatically record the technical data anyway — in that case, you only need to add the context.