FFTs or integer factorisation are pure-functional tasks and seem more suitable for a simple library call and local computation, without involving the network or

FFTs or integer factorisation are pure-functional tasks and seem more suitable for a simple library call and local computation, without involving the network or adding new external dependencies -- assuming you have code running somewhere with sufficient compute. i find APIs that let you interact with or observe the world far more compelling (e.g. get the latex forex rates, make a phone call, etc), especially if they put a nice stable interface in front of a lot of complex or evolving details you'd rather not have to care about.