Once you've learned what is necessary to, say, modify already-existing applications, you should be familiar with monads and some basic monad transformers like ReaderT.
Once you're there, I don't think 'choosing an effect system' is a perilous question. The monad transformer library, mtl, is an effect system, the second simplest one after IO.
> Once you're there, I don't think 'choosing an effect system' is a perilous question. The monad transformer library, mtl, is an effect system, the second simplest one after IO.
I'm aware of that, generally when people say "choose effect system" they mean choose some algebraic effect system, all of which (in Haskell) have huge pitfalls. The default should be monad transformers unless you have some exceptional situation.
This isn't really true. Bluefin and effectful are effect systems, but not algebraic effect systems.
I should have mentioned that, as you say, monad transformers should be the default effect system choice for 99% of people