My children don't have arbitrary limits on their time spent on the computer or watching television or daydreaming.
People often say things like, "If I didn't limit screentime, my child would just stare at a screen all day." There is a lot of educational value in computer games, video games, YouTube, TV shows, documentaries, and movies (yes, even the ones that aren't billed as educational). However, given an environment of support and interaction, with interesting people, places, and things surrounding a child, even the most die-hard fans will participate in other activities as they find them engaging. I love that without limits TV and computer use can just be one more option, as can wiffleball and audio books and building forts in the living room.
If you're interested, there is a short article written by Pam Sorooshian on the Economics of Restricting TV Watching of Children. Marginal utility, anyone?