Left standing in the first pour, on purpose
When a footing goes in first and a wall gets formed on top of it later, the crew sets dowels into the top of the wet footing before it cures, spaced to match the wall's vertical steel and left sticking up the length of a lap splice. Once the footing sets, those bars are what the wall's steel gets tied to, so the two pours act as one connected piece instead of two unrelated slabs of concrete stacked on each other.
Dowel or keyway, two ways to lock a joint
A keyway is a groove formed into the footing that the wall's concrete keys into when it is poured. A dowel is steel crossing that same joint. Some jobs get one, some get both, and which a footing needs comes off the plan and the engineer's detail rather than a habit either way. Either move is solving the same problem. A joint between two pours is a plane where the wall could slide or separate if nothing ties across it.
Where else a dowel earns its keep
The footing to wall joint is the most common place to find one, but it is not the only one. A new slab tying into an existing one, an addition's footing tying into the house's original foundation, a driveway apron meeting an older drive, all of those can use dowels drilled and epoxied into the older, cured concrete so the new pour has something to grab instead of just butting up against it. Without that connection, two slabs poured years apart simply sit side by side, free to settle or shift at slightly different rates, and the seam between them is where that difference shows up first.
Getting the spacing and embedment right
A dowel that is too short does not develop enough strength on either side of the joint to do its job, and one set at the wrong spacing leaves gaps in the connection. Bar size, spacing and how far it has to run into each side of the joint come off the structural drawings, the same way the rest of the steel does. We do not size that on the fly.