No cage needs to have a run attached provided the cage itself is big enough.
Any cage used indoors which is not big enough in its own right would always need a run to be attached to it to give them enough space. It can be useful to do this to save someone having to buy a whole new cage for example if they were sold a cage in a pet shop which they later found out to be too small. C&c grids can be attached to the front to increase the cage size and then the original cage door is permanently left open to allow constant access.
This is where being inside has its benefit - additions can be made easily.
If someone gets an outdoor hutch which is not big enough you can’t easily add anything on to the front to make it big enough. This is usually due to weather proofing and the fact outdoor piggies need a lot of protection. It may also make it insecure and more at risk from predators.
It would usually mean getting a whole new hutch of the correct size.
In terms of hutch/run combos (which is what I think you are meaning), outdoor hutches do not need to have runs attached (either the ones which are in front of the hutch or the ones which are a hutch on top and the run underneath accessible via ramp) and actually I would advise that they are not attached.
Attached runs can make them hard to move around to a fresh patch of grass, have the potential to add a point of insecurity, and they can also make it hard to access the piggies (youve constantly got to climb in it to get to them, and if they’re out, a risk that you may accidentally hurt the piggies getting in the run).
I have completely separate runs and physically move my piggies back and forth from their hutches in the shed into the runs on the lawn when I’m there to supervise and when weather allows.