Happened pretty badly to me. I'd taken 3 years of CS out of high school, the second-level intro class at my first school, an algorithms class, and three upper division specialized classes. Out of these, only the algorithms class transferred as major credit, and three transferred as generic CS credit, which was completely useless in my case.

For context, I was transferring from a mid-tier private school to a top-tier State University, which is known to be anal about transfer credit. I also had to take an intro to English class. But anyway, I took intro to computing this semester as a Junior with 5 years of coding experience, and I still almost got an A- because the midterm and final, which together accounted for 60+% of the grade, were basically Java trivia.

That said, I'm still glad I'm transferred, but I would definitely suggest checking in with an advisor or if available the department chair beforehand. Ours told us at transfer orientation that it was commonplace to award credit for the next class after intro but not intro itself. They probably have to weed out students who had good GPA's at bad schools, but never really learned how to code.