Class file name case-sensitivity

So in the CI2 to CI3 upgrade instructions, it says to change Library, Controller and Model file names to be upper-case first.

Due to GIT ignoring case-sensitivity by default, by files were being pushed with lower-case names.

After switching between some branches, my newly renamed upper-case first file names had been replaced with lower case names.

Oddly, the CI3 installation still worked?

Is this due to me using Google App Engine on Windows? And not a typical LAMP stack on Linux?

What are the repercussions if I don't give file names an upper-case first file name?