My understanding is that, at least of the reasons put forward publicly, it was the concern about amber-lighting. It was the fact that it was a system that might have been used in order to flag politically sensitive or otherwise problematic access to information requests for special attention or special treatment. That may in fact have completely been the case.
But in connection with your previous question about efficiency, one of the advantages of a system like that, which keeps track of access to information requests across the country or throughout the federal government and crown corporations, would be in order to determine what sort of information is being asked for routinely.
If you think of the incremental cost of having to deal with an individual access request for the same sort of information over and over again, contrast that to having a policy within a government department or across the government to proactively disclose that information on a monthly basis--all policy documents related to whatever--and put them on a website. All of a sudden you're taking information out of a system that's currently overburdened and putting that sort of information disclosure into a completely separate column that's more efficient.
One could also keep track of on what date the request was received and on what date it was responded to, even at the largest level, in order to call to account government as a whole and also individual departments for the amount of time that it is taking to process these requests.