[jondubois]

>> Hence, we try to isolate business logic from effects and implement the former as pure functions.

This is a valuable insight. Especially if your main programming language supports both functional and procedural and/or OOP approaches; This statement offers a good guideline as to where the boundary should be.

I find that functional programming is great for business logic but not as great for more concrete logic where performance is important. For example, when dealing with low level concrete objects like sockets.