Location

The Location field can be used to supply a location to be recorded with the populated time entries.  When this field is enabled/selectable, the Location drop-down list will contain a list of all valid locations for a particular project.  When this field is not enabled / selectable (ie you are using the user's default project option), the user's default location will be recorded with the populated time.   Should the user's default location not be on the list of valid locations for the project, the user will appear as 'Missing' and you will not be able to populate their time.

See Admin >> Setup >> Location screen for additional information about generic Location defaulting rules.