Why we have to put ToList To List Object in c#

Why we have to put ToList To List Object in c#

List<Student> students=GetAllStudentData().ToList(); 

//Domain Object

now, I had Mapped To Business Object

List<StudentBE> studentBE=MapDomainToBusiness(students)

// as the MapDomainToBusiness() method returns .ToList() Object

return studentBE.ToList();

// Again Is It Needed To use .ToList() at return time //Here ToList Is necessary or not


Please let me now the importance of ToList