Often times your game will crash, and you have no idea WHY it crashed. NVAC can be helpful in preventing crashes, but the log doesn't contain useful information for the average to intermediate modder.
If you enabled the error log in NVSE, it can be of GREAT help in finding out what caused your game to crash. It can also help authors and users alike debug the mods they make and use. Bear in mind that not EVERYTHING in the log is an error, it could be just a warning, or giving some information on things that may be potentially buggy. Learning to read and understand the information present is on YOU to figure out, it's not hard generally as it's pretty verbose.
To enable the error log, go to your Data\NVSE folder. Open the nvse_config.ini , if it does not exist, create it. It is a standard text file. Make sure you have "hide known filetypes" disabled in your folder view options or you'll have a file with the wrong extension.
Add the following section and line with notepad or whatever you like.
Save and exit. Next time your game crashes you can open this log and scroll through it and be amazed at all the stuff that is broken in your mods, and maybe find out what crashed your game. :)
The log will be named falloutnv_error.log in the Fallout NV root folder.