Some schools require students to complete summer projects to assure they continue learning during their break, it's a good way to keep students prepared for the knowledge they will be learning in their new classes. Teachers setting up their projects for their students is a much more organized decision than rather having the students design it themselves.

Me being a student I find it easier for my teacher to post the directions online, its faster and just incase I need help on the assignment, I can ask one of my classmates who have the class or are planning on taking the class for extra help if needed. Teacher-designed projects are also easier for the teacher to understand, for example, during the summer I had two summer projects and both of them were created by my teachers, once they were turned in by majority of the students, they were quickly graded and in the grade book. Having the directions already sorted out saves you a lot of time and saves you a major headache because you'll already have somewhat of an idea of what the professor expects from their students, as well as it's easier for them because they'll already have known everything thats supposed to be done and could help you understand if you didn't meet the requirements.

From a teachers prospective, it might be easier for them to come up with an idea for a project because you don't really see a lot of student-designed projects, usually professors have detailed instructions on what, and how to do an assignment. Throughout my high school career, the only project I've ever had to construct myself would be an essay in an English class, other than that I've never been faced with an assignment that wasn't created by the teacher. It's a teachers job to make assignments for their students, how is a student supposed to learn if there isn't a set of well-planned directions for an assignment taught by the teacher?

In conclusion, I feel as though teacher-designed projects are cleaner and understandable for their students, it saves time for both parties, and it allows students to get a brief preparation as to what they will be learning in the nearby future.