It helps to reduce the maintenance time (as well as server resources since you aren't having to duplicate all of the files that may be uploaded as a part of the course as well).
Until Moodle gets a real CMS we use the store of course 1 for the big resources and we clone the remaining part of the course for our 9 local schools, using the same city-server.
We keep the group function for the classes. (We have big classes called "learning gardens" of 60 students on our schools.)
We use a modified php script - listening to the same Moodle password - for uploading resources in the subfolders of course 1. (see picture)
The red text explains how you can rewrite the resource-link into file.php code. NOT very userfriendly but our K-12 teachers can handle this
Another reason for removing big files from courses is that the import and backup-restore mechanisms always copy and merge the complete file stores of the other courses in your course...
I have been playing around with this same problem.
We have 4 classes who need to use the same material and quizes, forums uploads etc.
We are using groups within the same course, 4 groups each representing a class, when the students initially login they are given a specific enrollment for that group and they auto enrol in the group within that course, if you want you can further divide into smaller groups..
The advantage of this for us is that all grades can be separate for each group or viewed as a whole, also tasks can be done acrosss the grade or individually in each class or students can see other responses from other classes but not participate.
In the past we were using multiple instances of the same course or having all enrolled in the same course which was getting messy in the courses view .
How do you view just one group in the gradebook. We are using moodle 1.8 and this does not appear to be a feature. I cannot find the answer elsewhere but there do seem to be plenty of people asking the question.