Tab Settings is not an option for some Permission Sets
|Knowledge Article Number||000204537|
|Description||The Tab Settings section is missing from the Object settings for some Permission Sets. Some have them while others do not.|
|Resolution||The Permission Sets that are missing the Tab Settings section do not have a License Type assigned. When you first create a Permission Set, you have the option to assign it a License Type. When you do so, you will see the Tab Settings section is available under Object Settings | Object Name.
If you do not assign a License Type, then this option is removed. This is because some License Types, such as Chatter Free, have much less visibility to objects than say a Salesforce User. There would be an issue if you assigned that Permission Set to a Chatter Free User and had Tab Settings On for Objects they shouldn't see. The License Type on the Permission Set determines what objects are visible to modify permissions to.