@marilyn@mathstodon.xyz @coldkennels@mastodon.social The hfill would be fine if it's a local thing … In general and usually one would prefer having the same alignment for all those structures.
cases (which belongs to the amsmath package) hardcoded aligns the first column left. But you could define your own (or redefine it) e.g.
\newenvironment{Cases}{\left \lbrace \def \arraystretch
{1.2}\begin{array}{@{}r@{\quad }l@{}}}{\end{array}\right.}
would be the TeXnically cleaner variant to do that.