The short list
Live repair status, upfront estimates, one-tap digital approval, photo and video evidence from the technician, pickup notifications, full service history and loaner or shuttle scheduling. In that order.
Everything else — loyalty points, tire quotes, in-app chat — performs better once those seven are solid, and worse when they are bolted on first.
Approvals are the revenue feature
Digital approval turns a game of phone tag into an average response measured in minutes. Shops that adopt it consistently report higher approved-hours-per-RO simply because customers see the recommendation, the photo and the price in one screen.
Notifications need restraint
Send a push at three moments: estimate ready, work approved and started, vehicle ready for pickup. Anything beyond that trains people to disable notifications, and you lose the channel that makes the app valuable.