It is important that you insert in hoteliga all guests details.
This will help you have a complete and organised database of your guests so relevant reports will be complete and could help you reach any relevant conclusions.
The reports giving you information and details about your guests use the data entered at the "guests" tab of the reservation.
Depending on the country your property is located, you might need some reports for the Authorities.
The following reports might be useful to you.
47. Guests and nights per country for period
61. Guests currently checked-in
62. Guests (all-time)