When I install the module from Joomla administrator end, I found that many empty lines were added to PHP and CSS code files between each line.
Line1 Line2 Line3
After uploading to joomla,
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It's as simple as \r\n vs \n - text files deal with differently encoded line breaks depending on where you view them. The reverse can happen when you download a file and open it in various programs, and you'll find what was closed up online is double spaced in the editor.
Because each OS have different ASCII chars for linebreak, the combinations give different results when viewed on other platforms: windows = \r\n unix = \n mac = \r
It comes down to which editor the creator of the module used to create their files.
It doesn't cause any harm aside from readability.