The short answer: They don’t teach much.
An article from Texas A&M’s Eagle says:
Daugherity, a computer science and engineering instructor, is one of four senior lecturers in his department who has been given notice. The four represent roughly 10 percent of the faculty in the department; however, they teach a quarter of the classes, he said.
So they are 1/10 of the department and teach 1/4 of the classes. Who teaches the rest? TAs and tt instructors.
Lecturers are typically hired at research schools to lighten the load for tt people so that they can do the research.
The lecturer said:
“Our senior lecturers are highly qualified professional teachers,” he said. “Sure, it would be cheaper to replace them with a new graduate or even an advanced doctoral student, but I think it’s safe to say it wouldn’t be better for students.”
I was thinking they would probably use adjuncts.
However, that’s not what the Powers that Be say.
“We will have to make up for the loss in teaching power of the non-tenure track faculty by larger class sizes, and increasing the load on the tenured faculty,” Newton [dean of College of Science] said. “It will hurt to some extent the research and service they’re expected to do.”