When you're looking at fractions of a percent, remember to consider other options. Set up brotli, for example. Or redesign your site to have a leaner layout. You might not ever reach the efficiency level where optimizing optional tags is the best use of dev time.

And the overhead of tracking which tags are optional in which circumstances is not particularly small. Consider that the extra complexity could impede more optimizations in the future, especially now that your markup requires a more complex parser than it could have needed.