if u miss out 1 quiz , u miss out all the rest after it, its basically a free lunch.
It is useful because it covers the week's work with all the important points covered in the MC questions. It is a good measure of your udnerstanding in your weekly work, if u get nearly all right on first attempt it usually means u have done the readings and understand whats going on, if u get most of them wrong, it means u havent dont your readings thoroghly enough.
Yes 5% maybe little but think of it as a free lunch if u done everything right.