Nah - there are plenty of rather experienced and highly skilled brewers who never use a secondary fermenter.
Point of distinction - it is a "secondary fermenter" not a "secondary fermentation".
The theory is that you can help the yeast and trub precipitate out and clear the beer more efficiently by racking off to a second vessel. Its really more useful in winemaking where you can get some significant differences from leaving the juice on the lees in primary for longer periods before racking the juice off. Not such a big deal with beer, and often leaving the beer on the greater volume of yeast that's in the primary can have a beneficial effect on your beer in terms of cleaning up off flavors and stuff.
In the meantime, with all that said, I use secondarys for all my beer. 90% of the reason is to free up my primary fermenters for the next batch. If you're using an open top primary its a good idea to use a secondary to avoid things (bugs, microbes, children, etc) falling into it and also because after most of the active fermentation subsides its harder for the beer to maintain a protective CO2 blanket to avoid oxidation. Otherwise, I'm of the opinion that it isn't a big deal.
The reason that is commonly cited for moving the beer out of primary is autolysis - which is a point where the yeast basically die/eat themselves and create nasty (REALLY nasty) things in the process. I can assure you that you will never see autolysis. In fact - if you tried to purposefully get your yeast to that point it would take you the better part of a year and I would bet you that you still couldn't do it. IGNORE any autolysis warnings.
If you're going to rack into secondary, make sure you have your sanitation procedures dialed-in and wait until the krausen falls and move it to a vessel with limited head space - like 5g of beer in a 5g carboy. After the krausen falls there's little danger of blow off.
Gordie