A performance drag. Let's say you have an app that for N inputs creates N^2 state in memory... But now, if that's just what you must do for some reason, then,

A performance drag. Let's say you have an app that for N inputs creates N^2 state in memory... But now, if that's just what you must do for some reason, then, yes, immutability makes the task of taking all those snapshots real easy.