Attributes in Gramps
“The thinking behind dividing things into events and attributes was the following:
- The attributes are for something permanent, or at least somewhat permanent: eye color, blood type, etc. Usually you would have not more than one of each attribute type for a person/family/etc.
- In contrast, the events have a time frame associated with them. It does not have to be a fixed date, can be e.g. a span. So it is not unheard of people changing religion, property, and residence, etc. Each of those can be associated with the time period, and there can be many of the same type.
Does it make sense? I know this does not correspond 100% with GEDCOM, but we try to do what makes sense rather than just implementing a poorly written standard.”  -- Gramps-user mailing list
There is no clear boundary between attributes and events. Some will prefer having "Occupation" as an attribute, with no timespan; others, or in other situations, might find using an event more convenient.