Every so often, I get asked about whether it is really worth it to chase double quotes and constructs like
print "foo $bar baz", and replace them with something like
echo 'foo', $bar, 'baz', or even to remove all those big heredoc strings so convenient for large texts.
Of course, most of the time, spending hours to fine comb code in search of this will result in less of a speedup than rethinking just one SQL query, but the answer is still that, yes, in the infinitesimal scale, there is something to be gained. Even with string reformatting ? Yes, even that. But only if you are not using an optimizer.
Just don't take my word for it, Sara Golemon explained it years ago with her "How long is a piece of string" post, in 2006.