The way first year BE/BSc works is your science subjects also count as credit towards your eng degree. So instead of doing the eng maths subjects, you do the science version of it and that covers it. Also because I do 1st year chemistry I don't need to do a 2nd year chem eng subject next year because I've covered equivalent material. That being said I end up doing 1 or 2 less engineering subjects. For Science I can only do either 2 different majors or a double major and a minor in something else. The scieng degree ends up limiting some of your choice for the science bit, however to get your actual engineering degree, you have to do most of the subjects as that's set as part of the accreditted degree.