The idea of Decisions & Discussions is to help organisations make decisions. They can be simple decisions that people need to make everyday, to more complicated decisions that require collective input and discussion beforehand.
If they are "simple" they can go through a simple decisions process, where the decision is proposed and people can stake for or against using lazy consensus.
If it is "big" then it can be created as a Discussion. If a simple decisions requires more discussion it could also be escalated to a Discussion.