Choosing Branch development preferences requires all Rulesets in your Application to be locked. DevOps best practice is that the core rulebase ("the trunk") only evolves by adding non-breaking feature sets. This cannot be realistically achieved when an individual developer makes iterative rule changes that are visible to all members of the delivery team.
In Dev Studio this can be mitigated to some extent through the use of Check-Out, however App Studio simplifies the configuration experience by not requiring citizen developers to check out rules to modify them.
By locking the "trunk" and requiring all delivery team members to work in Branches, the scope of developers affected by iterative changes can be limited, and feature sets can become subject to Branch Review before being merged into the "trunk" where more stakeholders are affected.