What is the late round?
This technically isn’t a round – it is either mercy or desperation on the part of the school. If the school has so many applications it can guarantee complete class enrollment at goal and with the academic or diversity goals met, it is far less likely to have any late round. In this situation, allowing any late applications would be showing mercy toward an applicant. On the other hand, schools that are seeking substantial growth, those that are less selective within the applicant pool, and those with lower yield rate of admitted students that enroll are more likely to permit late applicants. This allows them to continue working toward the institutional enrollment goals (size, quality, diversity, etc.).
There may be penalties for being late with application materials. Late applicants may no longer be eligible for some or all of the school’s financial aid support. Additionally, international students are sometimes required to provide independent GPA evaluations from approved organizations so the late application can be processed without delay. This would add cost and time to the application prep period.