Even if you are not concerned with the alcohol content of your brews, you should still use a hydrometer. In addition to telling you the alcohol content of your brews, it also tells when fermentation is complete and it is safe to bottle without the dreaded bottle-bomb. So even from a pure "safety" standpoint, a hydrometer is a great investment in home-brewing.
With that said, as you progress in your career as a home-brewer, you'll come to appreciate alcohol content and it's relation to the various styles of beer available and how your brewing practices influence both alcohol content and the quality of your brew.