Secondarys certainly have a purpose, but are really only required in special circumstances, like any beer that requires long-term aging (high ABV, lagers, sours), or special additions to the beer (fruit, woods, etc.).
For standard ales, the only real reason to use a secondary is pure cosmetics in helping to clear the beer. There are certainly lots of other ways to accomplish that goal as well without use of secondary, like whirlfloc/irish moss in the boil, gelatin, and cold-crashing.
If you don't care about the factors above on any given brew, no reason to secondary. Personally, I rarely secondary for anything I'm going to drink at home, but I often secondary for beers that I know are going to be contest entries.
Secondary is far from required, but don't let anyone tell you that you NEVER need them, because they have their purposes.