Except for btr-v1.0-1.3.0.json profiles in this directory are built into DART and Dart Runner, and are used in testing.
aptrust-v2.2.json is the official APTrust profile
btr-v1.0.json was the official Beyond the Repository (BTR) profile included in DART since 2018 or so. It's actually a pre-release of the BTR profile. See below for more info.
empty_profile.json is an empty profile that simply conforms to the minimum BagIt spec. This profile has two purposes. 1) It can be used in validation to tell you whether any bag conforms to the minimum BagIt spec. 2) You can use it as a starter template to build your own profiles in the DART UI.
The template btr-v1.0-1.3.0.json became the official BTR spec after the BagIt Profile standard moved from version 1.2.0 to version 1.3.0. This profile points to a different URL than btr-v1.0.json and includes a "recommended" attribute on some tags. It also includes some additional fields in the BagItProfileInfo section.