If you name the methods correctly (what they do) splitting actually helps readability of the code.
It is quite hard to read and remember what was in the beginning of 500 line method.
IE it can help to understand the intent and flow of the code, but also make it harder to debug. If I'm in a situation where I want to follow the exact instructions a large fraction of the code performs, a call stack jumping all over the place can be pretty frustrating.
