Re: I detest that
> @jake that's horseshit
Lusty, it is enough having to tolerate your ignorance without you doing the arrogant twat thing, so please wind your fucking neck in. There are people in here who actually know what they're talking about and you are not one of them.
With that said, it is helpful to recall that a topical Linux environment consists of a number of superimposed, and sometimes complementary, layers. In the case at hand, the kernel (Linux), the installed utilities and configuration (the distro), the desktop environment and the individual applications (such as file managers) are all involved in determining what is going to happen when you interact with a file. Typically, a combination of file permissions, attributes, file contents and possibly file extension will be considered when making that decision.
In general, however, if file extensions are used at all (and that usually only occurs at the higher layers), they will be used merely to disambiguate between similar types.
E.g., opening file.csv in a spreadsheet application and file.txt in a text editor, even though both are plain text files. Conversely, saving a PNG file as file.txt will still result in the file being recognised as an image and being opened in the correct application.
The extensions, as others have already told you, are there primarily out of habit and as a matter of convention. At the OS level they do not have any meaning, they way they do in DOS and Windows.
Source: Linux developer here.