In my work we use the scrum board for the registration of activities, however there is always a dilemma of what to register there, some colleagues want to register on the scrum board the email answer (even to create a new user story), arguing that both the reading and the answer cost them approximately one hour of work, others think that it is not necessary to do this, another example of the problem occurs with the analysis of the requirements (spikes) that remain several weeks on the scrum board without moving, this because it depends a lot on the availability of the users, some consider that it is necessary to have the record of this activity on the sprint board and others consider that it is not necessary because it is an activity that takes several sprints (weeks or months) to finish.

Searching the web and forums, I find a lot of discrepancy, some justify their response using a measure of time (if the activity costs more than an hour, register it) and others justify it using a measure of complexity (if the activity costs work in a matter of analysis or development register it, no matter how much time it costs you), but the answer still does not remain clear.

For what it leads me to the question, when is it considered reasonable to record an activity on the board and why?