OK as I’m struggling to understand this app, I have put together my understanding at this stage, which hopefully will help some in the same situaion 
EXAMPLES OF WHAT DEVICE CAPABILITIES (DC) can do for you
1°) Use of minor actions / info from devices
WHY WE NEED “DC APP”:
Many devices in Homey have both:
- a main action / info, which is usually showing on the device tile and is usable in a Homey flow because the developer has created flow cards for it. In a simple approach, no real need for the “DC app” here.
- a “side” action / info, not showing up on device tile, and for which the developer may not have created a flow card.
WHAT CAN “DC APP” DO:
SIDE INFO EXAMPLE: a weather device measuring temperature (main info) and CO2 level (side info):
- Standard device tile will display T°, but not CO2. “DC app” will enable to display both T° and CO2 on a new “DC app” tile.
- Standard flow cards will be available for T°: let’s say if T°<x or T°>y to create flows
- no standard flow card has been created to use the CO2 value and if you are not a developer you simply cannot use this value in a Homey flow. A “DC app” flow card will enbale creation of flow cards (to be used in Homey flows) using all device actions / info, using potentially advanced logic. For instance if CO2 level was on average >x in the past 24 hours
SIDE ACTION EXAMPLE: a curtain device has actions only to fully open or fully close.
- “DC app” can also enbale creation of a button allowing to open a curtain by 50% only for instance. This could also be done through standard Homey flows
2°) Group multiple devices:
WHY WE NEED “DC APP”:
- displaying info from multiple devices on a single tile is not possible with Homey. For instance if you have 2 temperature sensors, you cannot show T° from each in a single device tile.
- displaying action buttons from multiple devices is not possible in a single tile with Homey “standard”. If I want a single tile showing a button to open living-room curtains and another button to open bedroom curtain, I can’t achieve that.
- triggering actions from multiple devices from a single button is not possible in Homey “standard”. So if I want to open the living-room and bedroom curtain form a single button, I can with Homey “standard”
WHAT CAN “DC APP DO”:
INFO EXAMPLE: 2 temperature sensors in 2 different rooms
- “DC app” allows creation of new device tile showing T° for each room, or average temperature for the 2 rooms, or past temperature 30 min ago…
ACTION EXAMPLE: 2 curtains are separate devices a cannot be actionned together with Homey “standard”
- “DC app” can help by creating a single button to control (open / close for instance) multiple curtains at once. You can achieve the same results with other approaches (using regular Homey flows, or using group app for instance).
These are just a few examples to help real beginners understand what Device Capabilities can do for you
If I have made mistakes, please feel free to correct me
Thanks
