\big modifiers

[ffreyer]

\big, \bigg, \Big, and \Bigg can be quite useful to tweak the size of symbols. It would be nice to have them

[Kolaru]

That could be down by reusing part of the logic of \left and \right I believe.

[ffreyer]

Some examples where this (and/or \left. \right<symbol> can be useful:

\Big\langle \frac{\psi}{2} \Big| \phi \Big\rangle
\left. \frac{1}{2} \right|_{x \to 0}

I guess \phantom{...} also fits into this. From what I remember you can use it to get a size for \left .. \right block. And as an invisible element to resize via left or \right.