Bryant, D., & Richardson, A. (2015) have found that university lecturers at University of Canberra who have postgraduate certification in higher education teaching tend to have fewer failing students, but also fewer students with high results. The authors termed the lecturers with teacher training as "Damage Controllers" and those without as "Perfection Seekers". They suggest the former should be allocated to courses with low retention rates.
Bryant and Richardson (2015) offer no explanation as to why certification in teaching should correlate with numbers of failing students. It would be tempting to say that being trained in teaching results in a better teacher, who is able to help those students who would otherworld fail. However, it may just be a correlation: with those lecturers who believe they should help failing students being more likely to enroll in teacher training.
Also it may be that the results are influenced by what the individual lecturers perceive as the purpose of a university course. A university course can be seen as vocational: teaching the bulk of students what they need to know to do a job. The emphasis in vocational eduction is to get students to a level of competence: more than competent is a waste of resources. Alternatively a university course may be seen as a way to identify those students who are best able to undertake research and become universality academics. The emphasis in academic education is to identify the few top students for advanced study: what happens to the bulk of students is not of interest. The aim (vocational or academic) influences the way a course is designed and assessed.
As someone who has done teacher training, I am in the "Damage Controller" category. I see teaching as like being a triage nurse, focusing on those students who need help to pass, paying less attention to those who are likely to pass without help and those who will fail regardless.