The benefit of creating events, such as departmental meetings, on a group calendar is that everyone who's a member of the group can edit these events. This helps to avoid situations when a departmental secretary created a series of repeating meetings stretching for few months in her/his own calendar and then she/he left for another position, or is on extended leave of absence. In such cases, only that person, as an Office 365 chair of the meeting, can make changes to that calendar entry. But if this entry was created in the group calendar instead of her/his personal calendar, the new person in that position will be able to make any required changes.
Any member of the group can add entries to the groups' calendar either via Outlook Web App (OWA, portal.office.com), or using Outlook 2016. For more information and step-by-step instructions, please review this Microsoft article:
https://support.office.com/en-us/article/Schedule-a-meeting-on-a-group-calendar-0cf1ad68-1034-4306-b367-d75e9818376a?ui=en-US&rs=en-US&ad=US