Isolation joint versus expansion joint
The two overlap so much in everyday use that most people treat them as the same thing, and on a lot of jobs they basically are, a full depth gap with a compressible filler in it. Where the words split is what sits on the other side.
An isolation joint is defined by what it is next to, something that is not moving at all, a column footing, a manhole, a fixed piece of structure that was never going to shift with the slab in the first place. An expansion joint is defined by the job it does, giving room for two things that both move, just not at the same rate, to expand and contract without fighting each other.
Where an isolation joint goes on your slab
Anywhere a slab surrounds something that is not going anywhere. A garage floor poured around a support post gets one at the post. A patio poured up against an existing foundation wall gets one at the wall. A driveway poured around a drain, a utility box, or a manhole gets one there too, a full depth ring separating the concrete from the fixture instead of bonding to it.
Skip it and the slab tries to shrink and settle the way it normally would, and the fixed object holds one small section of it in place while the rest moves. That mismatch has to go somewhere, and it usually shows up as a crack radiating out from the thing that should have had a joint around it.
Can a control joint do the same job
No. A control joint is a shallow groove inside one slab, meant to manage shrinkage within concrete that is all moving together. An isolation joint is a full separation between the slab and something that is not part of that same movement at all. Cutting a groove near a post is not the same as isolating the slab from it, and it will not stop the crack a true isolation joint would have prevented.