Access more properties for an item
There is more that can be done to a note or group of notes than just assigning a duration, an accidental, a slur or the like. When you select a note (or group of notes) and press Alt+Enter, a dialog box appears to give you more control over the note. The Notation Properties dialog box allows you to change the spacing, mute the note(s), turn off ledger lines, change tie and slur direction, change the color, mark it to never be printed and more. For most any item entered (rests, bar lines, tempo variance, etc), you can select it and use Alt+Enter to access the properties dialog box for that item to have more control.
Inserting Items, why 1 tab and not 3
The difference is the setting for Tools: Options, Editor, Smart Properties Insert.
When enabled, the Visibility properties for new items are automatically configured with default settings. The Placement properties are set by finding a similar item elsewhere in the staff, and then using it as a basis for positioning the new item. If a similar item is not found, the program decides on the placement properties based on reasonable defaults.
When disabled, all available properties for new items must be set manually. The properties are initially set to whatever was used the last time this type item was added. Here you would get the 3 tabs so you can access all the settings. The 3 tabs are the item to insert, Placement and Visibility.