If your professors are submitting their own recommendations, then you should choose "no".
Some institutions provide a "letter service" whereby they collect letters of recommendation
for their students and submit them to the selected schools. This is usually in the context
of professional schools (medical school, law school), and result in very generic letters of
recommendation. The positive aspect is that the recommenders only have to write one
letter and do not have to worry about multiple deadlines; the applicant can also be confident
that all letters will arrive, as they are submitted by the third party. The negatives are, of
course, that the letters cannot be tailored to the specific institution, and cannot be modified
if the circumstances change during the course of the application process.