RB Logbook is very customizable. You can log whatever you want, because you can create new fields.
You can also remove or hide fields that you don't want. This is useful because when you hide a field, you can still access it for a particular flight.
Let's check the flight edit screen. here you have two icons on the top right hand corner of the optional fields sections. The left icon is to decide which fields you want to show for each flight by default.
The chevron arrow can be used to display all the existing fields, so that even when they are hidden you can still make an exception for a particular flight. Whenever a field has a value, it will remain visible, even for hidden fields.
When you tap the icon to edit the fields/times, the following screen will appear:
Here you can toggle which fields you want to see and which ones you don't need. There is an icon in the top right hand corner to enable further editing of the fields. This is useful for optional fields that you have created yourself, because you can then edit the field type (text, numeric, time, yes/no) and the name of the field.