LaTeX files are just ordinary text (ASCII) files. They are readable on every type of computer system, and once compiled the final product looks the same on every system.

Compare this with MS Word, where the final product looks different depending on what computer is used to open the file, where the actual file is saved in some obscure binary format that may not be readable in a few years, and where something as simple as this 350-byte paragraph requires a file 20 kb in size even without any special formatting.

The issue of portability is particularly important for archival scientific publication. To give a rather sad example: My Ph.D thesis (dated August 2000) was written in MS Word. The current version of MS Word will, with some effort, read that thesis: but the formatting is completely messed up, most of the equations appear as big red 'X's, and several key figures are completely missing. To add insult to injury, I have to BUY some rather expensive software to even get that much!