Although that given example seems pointless -- because it simply seems like it's the same as text replacement within a text editor. Two words -- code obfuscation. The #DEFINE allows you to refer to a "friendly" or "meaningful" name within your source code, but what gets finally encoded as the .FXP are the confusing ones. Even if you could decompile the .fXP files, the result is still hard to decipher.

Back when I used write a few programs in interpreted BASIC (the early 1980s), I would ofuscate my code in specific ways by running the tokenized .BAS file through filters that would obfuscate the variable names. In strategic locations within the code I'd place comments that read "DO NOT ATTEMPT TO MODIFY" and "DO NOT SAVE TO ASCII FORMAT" -- as you might already suspect, those comments were designed to tempt someone to doing exactly what it tells you NOT to do. And of course, if they didn't heed those warnings (and it didn't take long for them to do that), they'd soon discover that the program is now seriously broken (it would crash in many different places with syntax errors). Usually took two or three incidents that I would discourage the typical user from looking too hard at the program.