[Kentaurus]

That's right. It doesn't matter.
The query doesn't get executed if the option is disabled.

And no, the filesize is not an indicative. You may save *a little* memory by loading less code, and you save the 2E-5 executing time of the "if" instruction. The size of the file itself doesn't matter at all.

This is not really useful, because the performance "gain" is really really too small. You'd need to have a huge amount of traffic. Even with 5000 users online it would make no difference at all. Even with 10,000.........

This is not the correct way of doing optimizations. Turn debug mode, and check where the bottlenecks are. A large memory-usage query, a long running one, php code that has high complexity or too much recursion. Removing code that doesn't get executed anyway doesn't make any difference and it's only fooling yourself. Do some benchmarks and test by yourself.