It's to help prevent spam.
People (or bots) that would otherwise post a junk message every second, filling the boards with nonsense, are stopped (or at least, slowed) by the time limit.
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The 1 message per minute limit has been around for a long time. I used to hit it a lot.
Now, there is so much traffic on the forums, and so many people answering questions, that I don't respond to nearly as large a fraction as I used to, so I hit the limit much less often. When I do, I sit back, take a few sips of tea, and then resend the message. A few second delay is definitely worth it if it reduces the spam.
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Why not have a vote on it? then all of the Scratch users could decide.
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Toasty, sarcasm does not work very well on the forums. Your best bet is to treat every post as if it were serious, but not to waste much times on the ones that you think are unimportant.
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