That's a terrific question.
The purpose of the estimates is to provide authorities up to a certain level, and then there will be circumstances as the year unfolds that will impact a department's ability to deliver a program or service. It's important to understand what those factors are. They can be contractual delays, negotiations with third parties such as provinces or other jurisdictions, or issues in terms of hiring staff or filling positions. These are all important considerations that need to be understood in terms of ensuring that there is ongoing attention to the delivery of programs and services.
The lapse number in and of itself is not necessarily a problem if there is a good and valid reason that the money wasn't spent. However, it can be a red flag if there are issues with a department's ability to deliver on contractual agreements, to conclude negotiations with third parties, or to hire staff. This information is simply presented for ongoing discussion and review by parliamentarians.