If those functions are interchangeable then you potentially have to deal with exception control flow on every line, or even within a single line. It makes it very hard to reason about all possible paths through a given function and do things like safe resource management (e.g. you always have to handle the possibility of further exceptions in your exception-handling code path).
For system failures it's ok because the only handling you're going to do is retry at high level (and so even languages with an Either-oriented style tend to have some form of "panics" or exceptions for that kind of failure). But it can be a real problem when that also happens for "normal failure" paths like bad user input where you want to actually have business logic that handles and perhaps recovers from the failure.
For system failures it's ok because the only handling you're going to do is retry at high level (and so even languages with an Either-oriented style tend to have some form of "panics" or exceptions for that kind of failure). But it can be a real problem when that also happens for "normal failure" paths like bad user input where you want to actually have business logic that handles and perhaps recovers from the failure.