I have a promotion set for users who make 10 posts. They go from being a limited member to a normal member.
I set it to run every 1 minute. Will this effect anything?
Trial and error my friend!
Memory usage and CPU usage on the server will increase though.
I'd advise against it and rather run it every 5 minutes
I am doing the same thing on my site. However I set it to every 5 minutes, since my site is small, I haven't had any issues.
If your site lacks the activity for the promotion system to run smoothly, then I see not problem with it (though I will set it to something higher, like 5 minutes as already suggested). As your board gets bigger maybe you could increase the interval time between runs.
5 Minutes would be good for a small forum, Once you get bigger you can upgrade servers and be able to run with more load with less stress, so to speak.