Going through the house usually means the outside route ran out
Two situations put this question in front of people. The first is a pour that is inside the building anyway: a slab on grade in an addition that is already framed, a garage floor with the walls up, a floor going into a shell. The second is a back yard hemmed in on both sides, where the side yards are blocked and the front door genuinely is the shortest way to the forms.
Those two get answered differently. Concrete going inside a building is normal work for a line pump and it is a large part of why the machine is worth owning. Concrete traveling through a house on its way to somewhere else is a last option, and we would rather add sections of hose and go the long way around the outside than run a line across somebody's living room.
An unfinished house and a finished one are two different jobs
In a shell, the route is a technical question and nothing more. Openings are wide, there is no trim to catch a coupling on, the floor is going to be covered by the pour or covered later, and the crew can pick the cleanest line from the trailer to the forms. Door openings without doors in them are the easiest way into a building there is.
Once a house is finished, everything on that list flips. The opening has a door and a threshold in it. There is a turn on the far side. The floor between the door and the pour is a floor somebody paid for. The route stops being about the shortest distance and starts being about what the pump hose crosses and what it rests on for the length of the pour.
What the line rests on for the whole pour
Empty hose is a two person carry. Full of concrete it is a different animal, and it stays exactly where it was laid until the last yard is placed. That is the plain reason a route through a building gets settled before anything is on the road rather than worked out with a loaded truck idling in the drive.
So the crossings are picked on purpose and picked with you. A threshold, a step, a doorway, a stretch of finished floor. Each of those is a decision made on the estimate visit, when somebody can look at it, and the thing that helps most is you saying what you care about. A new floor, a fresh paint line at the base of a wall, a stair tread. Told in advance, the route goes around it or the crossing gets planned.
The turns matter as much as the distance. Getting hose through an opening is easy. Getting it through the opening and then around a corner in a hallway without a hard kink is the part that takes walking first, because a kink is where a line packs up and stops.
The alternative is what makes the answer worth having
If concrete cannot travel through the house in a hose, it travels through it in something else. A georgia buggy or a wheelbarrow makes the same trip, only it makes it forty times instead of once, with a wheel on the floor each way and a man behind it moving at a pace a chute is setting for him. A hose goes in once, lies still, and comes back out at the end.
That comparison is also how we decide. If the outside way in exists, even a long one, it usually wins, because a line laid down a side yard is not touching anything you have to live with afterward. If it does not exist, the line goes through, and we tell you exactly where it will run before we bring concrete anywhere near your address.