Why the Need?
Regular CTs won't fit in existing panels
But dedicated CTs are small enough to fit.
When high accuracy is needed
Dedicated CTs can be as accuracte as 0.3%, much better than the 1% of regular CTs.
Installing a CT w/o interrupting power
Split core CTs can be used, they can be installed easily w/o lengthy disruptions, reducing both time and effort.
Same circuit, but branching wiring
Small CTs allow for parallel connections.