Well, I think you need a minimum of two. Three is maximum, which is normally the case now.
One of the issues with the budget is that it could include various measures, or set-aside money, for certain types of proposals that the Treasury Board committee is still looking at but hasn't approved. Those types of things cannot go into the estimates for parliamentary approval until they have had Treasury Board approval.
So you are going to have supplementary estimates to reflect those types of changes in programs. In addition, things happen during the course of the year. You could have an emergency disaster. You may have to respond to certain types of events, and those events may have been provided for in a budget with money set aside. But because you don't really know what the event is, you can't approve it beforehand. This would have to be done during the course of the year through supplementary estimates.
But I think if you were to table estimates in advance of the March 1st supply period, or deadline, then you would get a lot more of the spending into the estimates than is currently the case.