I was sure that I was loggedin and pressed search button to get needed info, but I was wrong; I was logged out. Then I logged in and I was told, that I had nothing inputed in the search bar...Now I need to wait 90seconds. It is not much, but still...
Yeah, this is done to prevent abuse from people with bad intentions.
Say you have a bot that created a hundred newbie accounts, which also use the search function, causing the server to lagg ( because it needs to index so many posts), essentially DOS'ing itself.
Once you rank up, this limit gets lower ( less seconds).