If would be nice if all the materials of Codeforces contests were publicly available and there was possibility to download the archives. There may be some reasons for it:
It's easier to hold trainings. There can be different problems on trainings and it can be good to collect them in one contest on one testing system. If the tests are open, it can make holding trainings in this way highly easier.
More availability. If the site is down or gone offline for some time, contest materials may remain and there will be a possibility to test problems locally.
More safety for problems. Problem materials will be stored not only on Codeforces. If some problems will be lost on servers for some reason, it will be easier to restore them.
There can be a counterargument against opening the tests that not experienced users will download tests instead of finding bugs themselves. But 1) small tests are already open and 2) the access may be given only for users that have coach mode.
It will be better if MikeMirzayanov opened the materials. I am waiting for his response to this blog post. But I want to open the materials of my contests without waiting for his decision: