I’m a programmer that is new to UX and have a potential web project that has probably ~5k pages.
What type of information could I take away and benefit from this tedious exercise?
I agree with the above response conceptually..however, using the right tool to automate the tedious task of generating a visual sitemap of 5k pages would perhaps be both a more efficient and thorough solution for your needs.
You don't want to have a full sitemap of 5k pages.
You want a summarized view of your website.
Showing too many complex interactions or links between page is not necessary. You should have a clear understanding of the website's structure when looking at the sitemap, but it's not necessary to be exhaustive.