Generic element tag selectors also bad for reasons besides perf

[cvrebert]

The current guidance in the Guide is:

• Use classes over generic element tag for optimum rendering performance.

But there are non-perf-related reasons to avoid them too, right? Like why we're trying to avoid them in Bootstrap going forward?
e.g. They're unnecessarily constraining in some cases. Maybe my component uses an h2 today, but tomorrow I might want it to use an h4 instead, so it's annoying if the component's CSS relies on this aspect of the DOM.