Some keywords should
be bolded to point the search engines in the right direction.
When you are writing your web pages you will probably want
to stress a certain word or two. Unlike header tags, using
the <b> option in your html code to make a word stand
out doesn't carry as much weight with the search engines.
Don't discount it though because it does matter.
Any time you stress a word and make it stand out you are also
stressing that word to the search engines.
Using Bold Text should be done whenever it fits into
the flow of your content and will match the look and feel
of your website.
Many WYSIWYG (What you see is what you get) programs do this
for you on the fly, but make sure you end up with clean website
code.