Whether to use a secondary fermenter or not has become a religious argument. IMHO it depends on what you're trying to do. I brew simple low gravity session ales (no fruit, no dry hopping, etc.). I've never used a secondary. I let it sit in primary for 2-3 weeks, then bottle, let it sit for 2-3 weeks, refrigerate for a few days, and drink. Depending on the style of beer it may or may not get better with really long conditioning times. As Puddlethumper said many of the bitters and milder flavored ales taste better fresh.
I've heard experts say that there is nothing that can live in beer that can harm you. It might not taste very good, though.