Upgrade W7 to W8 - backup needed?


I have some questions about the option to save your files in the upgrade assistent.

When I check the box to save every app, etc. Does it truely keep everything? Because on some website I read that windows decides for me whats important, wouldnt want that to happen.

My external HDD just broke down when I was installing windows... That luck. Therefore I have no option to make a Back-up until I get a new drive.

Hope someone can answer it!

TLDR; When I upgrade w7 to w8 do I retain all the files I had on w7?