I dislike it (and most forward-thinking companies wouldn't risk scaring off people who are the type that work on their own time), however I can see the reasons.
How do they know you did it at home, not during work hours? How do they know it didn't affect your work? If you're salaried, there aren't set start/stop times. How do they know they weren't paying you at the time you came up with the idea, or thought through a problem? Did you do it on a work laptop? Did you use a copy of Photoshop that work paid for? Is it something you did for your job, and now you want to sell it to other people -- even if the code has been rewritten?
Again, I don't think it's very enforceable or even a good idea. However, I can understand why a lawyer would slip it in.
How do they know you did it at home, not during work hours? How do they know it didn't affect your work? If you're salaried, there aren't set start/stop times. How do they know they weren't paying you at the time you came up with the idea, or thought through a problem? Did you do it on a work laptop? Did you use a copy of Photoshop that work paid for? Is it something you did for your job, and now you want to sell it to other people -- even if the code has been rewritten?
Again, I don't think it's very enforceable or even a good idea. However, I can understand why a lawyer would slip it in.