A few extra bricks are a boon in a set of Lego. Likewise an extra couple of tent pegs, an additional screw or a back-up pen. They’re useful because you know exactly what to do with them – and what not to.
Extra parts aren’t useful when it’s not clear what they’re for – when they make you worry that you’ve overlooked a crucial step in a process or used the wrong part.
First clarity and simplicity, then extras – but only if they don’t muddy the waters.
Less is usually more.