Here is a copy/paste from an earlier post of mine:
LaTeX and Word are two different ways of doing the same thing - producing a good looking scientific paper. They each have their advantages and disadvantages. I've worked with both during my schooling and here are the points that I found to be the most important (in no particular order):
1) Working on multiple computers: Word wins. I can take my document to virtually any computer in the world, and it will be immediately useable (especially if you save in an older format). With LaTeX, if I want to bring my work to a different computer (such as a different school lab) I need to download some version of TeX. I might not have permission to install TeX, I might not have the time to download the huge numbers of files, I may have trouble finding versions of TeX that will work on each different computer...
2) Group work: Word wins. What if only half the group understands Tex (I can imagine the look on my grandmothers face if I ask her to help type a family letter using TeX instead of Word)? What if some group members cannot download it? Word has many built in features that assist with multiple authors. The best you can do in TeX is to put comments listing the author of each sentence - but that really clutters up the source file. Also I can't count the number of times I was in a rush to finish a group project and found out that the disk with the project on it didn't have all the necessary files (fonts, formats, individual files for every single picture, etc.) meaning that I had to quickly drive from campus to the person who has that file.
3) Viruses: TeX wins. Word has many 'bugs' that are actually computer viruses. The must frustrating and one of the most common is the 'out of disk space' error. When this occurs it is difficult to save your file and most people give up and lose their data (although there is a simple workaround). This isn't a Word bug, but your computer is infected with a virus. TeX itself is basically immune from these. There are other examples, TeX wins in all.
4) Debugging: Word wins. Since TeX code must be converted into a viewable format you must code it properly. If you aren't skilled at computer programming, I wish you luck. It can take hours searching through a TeX file filled with complex symbols and code until you find the improper code that won't let you see your work. It is a viscous circle. You can't see your work, so you don't know where you messed up, so you can't edit it, so you can't see your work... With Word there is no debugging of code since there usually is no code (few people do any sort of Word macro work).
5) Learning curve: Word wins. Go back to my grandmother example. I truely think she would give up computers all together if she only had TeX to write letters with (assuming she could even figure out where, what, and how to download to use it in the first place). With Word, all you need is basic computer knowledge and you are up and running.
6) Cost: TeX wins. Assuming you have internet capability, TeX is virtually free. Although Word document viewers are free, Word itself often adds to the cost of computer purchases.
7) Writing time: Word wins. Due to #4 above, it is highely undesireable to write large sections of TeX code at once. Thus you must write a small section, save your file, load a TeX viewer, wait for it to be compiled, see it has errors, edit your TeX source, recompile, then you see your work, repeat until you like the outcome. With Word, you see what you get as you type it. The result is a document often takes 2-10 times as long to write in TeX.
8) Finished document: tie. I can get the exact same result with either so neither have any advantage.
9) Working with multiple programs: Word wins. Suppose you need to create a document with text, line drawings, pictures, and graphs. Word can create the line drawings, for the graphs you go to Excel (or similar program) and hit copy and paste, for the pictures you just hit insert picture. Need to change data on a graph? Just update it in Excel and it is automatically changed in Word. TeX is much more difficult. There is no built in drawing program. You must save the graphs as pictures and write code to load them in (meaning that the graphs are then uneditable if you get additional data, you must regenerate them, and resave them as another picture). Also all these individual items reqires another file that you must remember to copy (see #2 above).
10) Conversions to other formats: Word wins. Suppose you need your document as a webpage, as a PDF (assuming you have the PDF writer), as a Lotus 1-2-3 document, as an easily readable text file, or even a TeX file, etc. just hit 'Save As' in Word and you are done. Converting a TeX file to any other format can be quite a nightmare in time and expense. Note: due to easy converting, this eliminates the fear of outdated document formats that someone above mentioned.
There are other advantages and disadvantages of each, but they are minor compared to the top 10 I listed above.