Hello!
I used the term “server resources” to directly refer to “memory”. TSF uses more memory for memoization to improve the load times. As long as you don’t run into memory issues, you’re fine. After all, unused memory is wasted memory.
With the advent of PHP 7, it’s an entirely moot point. The memory consumption of PHP 7 is less than half of what PHP 5 used to consume, and we haven’t heard anything related to memory issues in a couple of years.
With that said, TSF remains the fastest full-featured SEO plugin out there. Every update we work on this, and TSF v4.0 will even be about twice as fast compared to v3.2.4. Then, it’ll only add 0,0003 seconds to your page load time (using PHP 7.3). We can’t see any other SEO plugin beating that time soon, if ever.
More on that will be explained in an announcement blog post soon. Cheers!
