Again I direct you to my previous post where I cover developers not having the time to familiarize themselves with spaghetti code.Why?
If you dont understand the code, what is documentation gonna do?
There's a reason it's called spaghetti code, it's complex, often counter intuitive, implements the same logic multiple times and especially, poorly structured, devoid of useful commenting, when left to an intermediate developer, over-engineered, because intermediate developers like to look clever. To understand that code is not something that happens overnight, it can take months to reach a point where you know where (almost) everything fits in and how it all holds together (or not).
Personally, I prefer well written and commented code to documentation. But with spaghetti code, you won't get useful commenting in code, and instead most of the comments in a code base will simply be of dead code that got deprecated along the way but never deleted. Of course, you can go through the process of familirizing yourself with the code, but until then development and bug fixing will be slowed, which is where documentation, however limited, can literally shave weeks from this process. Suggesting that you'll magically understand the often contradictory logic of a million lines of code, is dangerously naive.
Because ultimately if you're not going to be in the company that long, if your average lifespan as a developer there is six months or a year, then you're going to lose that familiarity and start over from scratch with every new hire.