Q: Why does my iTunes analyze the same songs upon opening?

iTunes version 12.01.26 (happened also on previous versions)

This is more of an annoyance than a real problem: every time I open my iTunes, the same songs (pre-existing and imported) are analyzed and determined for gapless playback. Why?

I don't see the reason the same songs - that already exist in my library - have to be analyzed every single time I open iTunes; it's thousands of songs, not just a couple.

Maybe it's the way/location I have them stored, but I'm not certain of that and I'm also not sure where/how to look.

Help!