From a historical viewpoint, Siegel and Shuster planned on Clark sharing his secret with Lois in the '40s. DC, in their infinite wisdom, wouldn't let them. I think it would have been interesting if Lois had always known that Clark and Superman were one and the same. It would have saved readers from decades of stories where Lois schemed to prove Clark is Superman. (Sure, some of those stories are fun, but it's hard to take Lois seriously as a reporter -- and some of the best Clark and Lois stories are where they compete with each other even as they work together -- when she's acting like a busybody.)
We live in a society where people assume that they need to know everything about everyone, and social media magnifies that assumption (come on, admit it -- even Santa Claus would be under suspicion of having ulterior motives for doing good deeds!). I have a hard time understanding why the world needs to know that Clark Kent is Superman. However, simply because they are good friends, I also don't understand why, in the 21st century, Clark hasn't trusted Lois with his secret. There are times when even the most powerful person in the DC universe needs a trusted friend to talk with about things.