The .net framework is aset of programs provided by MS containing programming items that can be used within other programs such that the other programmer does not have to write them themselves (Put simply). Whether you need them is dependent on whether you are running any programs that require a ,net facility. Unfortunately it is not easy to determine this unless the programmer states this in the program description. An additional problem is that any such program mat require a specific version of .net so it is probably easiest to just install them all and keep them all updated. Its a pain I appreciate as these tend to be the biggest updates that take the longest time. If they are not being used they do no harm.
Sony Xperia Z5 review: Hands-on with the phone which the Z3+ should have been