Why does Superman need a secret identity? I mean, he's Superman. So what if people know where he lives? And where does he live? I haven't read the comic book in decades, but do we ever see Clark Kent in his lonely little bachelor apartment, listening to Morrissey on his CD player and mooning over Lois? Or does Clark just pop into the janitor's closet after work, change in to his Superman uniform, and fly off to his Fortress of Solitude, where he sits listening to Morrissey and mooning over Lois? Maybe he's too busy fighting crime in the evenings to moon Lois. I mean moon over Lois. But if that's the case, when does he find time to sleep? For that matter, does he need sleep? He's Superman, after all. What about food? Does he get enough fiber? Would he be afraid to eat at Taco Bell? Clearly I'm out of the comics mainstream, but I'm sure those who are in it can answer those questions. But don't bother.
I haven't read many of the comics, and there are enough Superman retellings to suit everyone, but I've always preferred the idea that Kal-El was raised as Clark Kent, hard-working son of salt-of-the-earth folk, so he aspires to the same things humans do: a fulfilling job, friends, relationships, family. To attain any of these, he needs to assimilate as well as possible. In other words, Clark Kent is his major identity, who he wants to be, and Superman is who he feels a duty to be. He puts on the tights and cape as a police officer puts on a uniform.
Another reason he needs to work at the Daily Planet is to keep abreast of what's going on in the world and, as Brando's Jor-El put it, discover where his strength and power are needed.