Unless you are racing, I can't imagine not using my cleat covers because they take up too much space! I shove them in my jersey pocket vertically, and can also put my little wallet or cellphone in there, too. And that's just one pocket.
It always surprises me that people don't use cleat covers for Speedplays. While I don't walk far in my road shoes, I do stop and get lunch, use restrooms on my rides. I still replace my cleats once a year and use White Lightening to lubricate them every few rides. My left one, always gets a little finicky, since i always clip out on that side. I know I shouldn't, but it's the way it is. I ride 2,500-3,000 miles a year.
The importance of cleat covers was driven home after we finished a ride that had a lot of rain at the end. We were on a tour and walking into the hotel when my DH slipped and fell in the lobby because of his wet cleats. He had forgotten to put the covers on. After a million employees came to assist him, probably to make sure they wouldn't get sued, he was really mortified. And he had a huge bruise on his hip the next day.
I know many people that use Frogs on their road bikes. It seems to be a good solution for many. My second bike has spds and my knees always feel it when I ride that bike.