In English, we use capitals in the following situations:
<ul>
	<li>At the beginning of a sentence.</li>
	<li>For proper names (Deborah Brody lives in Maryland)</li>
	<li>For titles (President Barack Obama)</li>
</ul>
We do not use capitals as a way to emphasize words, or make them prominent. For that purpose, we might underline,  italicize or bold the word in question.

All caps as in NO WAY AM I GOING OUTSIDE TODAY is generally used to denote excitement, anger or "shouting."

However, I see words being capitalized that don't need to be, all the time.

Notice this help wanted ad from Craigslist (words underlined for emphasis by me):
<blockquote>Our <span style="text-decoration:underline;">Firm</span> has an immediate open for two<span style="text-decoration:underline;"> Writers</span>/<span style="text-decoration:underline;">Proofreaders</span>
We are very flexible:
You can work as contractors, <span style="text-decoration:underline;">Part Timers</span> or <span style="text-decoration:underline;">Freelancers</span>
You can work from your house/office or/and our office
You must have experience writing for <span style="text-decoration:underline;">Finance</span>, <span style="text-decoration:underline;">Tax</span>, <span style="text-decoration:underline;">Accounting</span>, and <span style="text-decoration:underline;">Insurance</span> businesses
You must have experience in <span style="text-decoration:underline;">Marketing,</span> A<span style="text-decoration:underline;">dvertising</span> and<span style="text-decoration:underline;"> Sale</span>
You must be available to start next week
You must include your desired pay (per page and/or per hour) in your email or cover letter</blockquote>
This is a help-wanted ad for a proofreader! I am not sure the ad is intended to be a test or if it is showing (unwittingly) a desperate need for a proofreader.