Pace it off from where the truck can actually stop
Stand where a loaded ready-mix truck could realistically park, not where you wish it could, and pace from there to the far corner of the forms. That distance is the number that decides this. If it is inside about 10 to 20 feet and the ground falls away from the truck, the chute will very likely do the job and you do not need anything else brought to the site.
Most people measure from the road and get a comforting number. The truck does not stop at the road. It has to back to a spot where the drum end points at the forms, on ground solid enough to hold it loaded, and that spot is usually further from the pour than the road frontage made it look.
The chute runs on gravity, so downhill is half the answer
A chute is a steel trough. Nothing pushes concrete along it. It moves because the chute is tilted down and the mix is wet enough to slide. That has two consequences worth settling before pour day.
First, the forms have to sit below the discharge point. A slab uphill of where the truck can park is out of reach at any distance at all, because the concrete has nowhere to run. Second, the flatter the chute has to lie in order to stretch to the forms, the slower and stickier the flow gets, and the more of the pour gets spent shoveling concrete along a trough.
That second one is where mixes get ruined. A crew fighting a long flat chute is tempted to add water at the truck to make the load run. Water added at the chute raises the water cement ratio, and that comes straight out of the strength of the finished slab. It tends to show up later as a chalky surface that never quite hardened. Ten more feet of reach is a poor trade for that.
The last twenty feet, and what people do about it
When the chute comes up short, the concrete still has to travel that distance somehow. There are three usual answers and they are not equal.
Wheelbarrows work. For a small pad, two people can move a yard or two without much drama. Past that the labor stacks up fast, the pour slows down, and a slow pour finishes worse than a quick one because the first concrete placed is already setting while the last is still coming. A georgia buggy, which is a powered concrete cart, carries more per trip, but it needs a firm and reasonably flat route to run on.
Neither one helps at all when the route crosses a lawn, a septic field, fresh landscaping or the top of a bank. Those are the sites where the distance is not really the problem. What is between the truck and the forms is the problem.
Where the hose picks up the difference
We own a trailer-mounted line pump and run it ourselves, with an operator at the machine and a hose hand at the placement end. The truck backs to the hopper wherever the ground is solid, and 2.5 or 3 inch line carries the concrete the rest of the way. Concrete moving under pressure does not care about grade the way a chute does, so the hose goes uphill, around the corner of the house and through a standard yard gate.
That covers the backyard patio behind a fence, the basement floor inside a wall that is already standing, and the footing at the bottom of a bank. All three are past a chute at any angle you can set one. On our own pours the pump is part of the crew rather than a separate arrangement to make. On another contractor's pour we do the pumping for them, our machine and our two people, on their schedule and their forms.
And when the chute will reach, we say so. Bringing a pump to a pour that did not need one is setup time and expense nobody got anything for, and that is an easy call to make on the phone.