Non-obligatory permissions refers to those things that a person may do, but does not have to do. It refers to choices such as which career to enter, which television shows to watch, what to eat, and whom to marry. In these areas, a person can do as he or she pleases - and there are many and strong reasons to hope that different things please different people.
The term "non-obligatory permissions" is used to distinguish them from obligatory permissions. Repaying a debt is both obligatory and permissible. Telling the truth under oath is both obligatory and permissible. In fact, it is not unreasonable to argue that everything that is obligatory is also permissible. (There is one sense in which this is not the case that will be covered separately under "moral dilemmas".)
Some theories have trouble with non-obligatory permissions. Act-consequentialist theories such as classical utilitariansm allows for one obligatory action (the action that produces the best consequences) and a long list of prohibited actions (everything else).
Act-consequentialist theories try to make room for non-obligatory permissions by arguing that we often do not have the ability to know which action is best. However, this permissibility is based on ignorance. It vanishes as soon as the ignorance is removed. It does not allow for genuine non-obligatory permissions. Desirism, on the other hand, holds that there are some desires that people generally have no particularly strong reason to promote or inhibit and, in some cases, people have reason to prefer that others adopt a range of desires. These are in addition to desires that people generally have many and strong reasons to promote or to inhibit.
Imagine a couple in which one of the partners prefers white meat over dark, while the other prefers dark meat. When they cook a chicken, the first partner gets the breasts, while the second partner gets the legs and thighs. These two people have desires that are in harmony with each other. Not only is there no particular reason to promote a universal desire for white meat or dark meat, there are actually reasons to prefer that each partner have different tastes. With the current situation, there is no competition for "the good pieces" of chicken, and neither person has to settle for second best.
On a larger scale, identical tastes in food result in scarcity and competition. If we all had a strong preference for the same food, one of the effects would be that the preferred food would have to be grown on more and more marginal lands. All of the best land would be used up quickly, followed my land that is not quite so good, and, ultimately, land poorly suited to growing the desired food gets used.
However, a variety in the taste for food results in a variety in the production of food. Land that is unsuitable for one food can be used to grow something else better suited to that land. There is less competition, and fewer people have to settle for second best because everybody else is fighting over what is best.
The same analysis applies to finding a career or a mate. A society would tend to be much less off if everybody liked being an engineer and hated teaching. There would be a lot more competition for engineering jobs. This competition may force some people into teaching against their will. A lot of these teachers would be poor teachers because their hearts are not in their work. They would rather be engineering something.
In a society where some people like engineering and some people like teaching, more people get to enter a profession that they actually like, and fewer people need to select the second-best option.
These are cases where people generally have reason to give people the liberty to choose among a wide variety of options and to hope (and encourage) people to choose different options. This implies giving people freedom among a range of likes and dislikes.
This is not a non-obligatory permission built on ignorance. This is a genuine non-obligatory permission - a freedom for the individual to choose based on personal likes and dislikes. Non-obligatory permissions arise from the fact that morality is primarily concerned with the evaluation of desires, and the fact that there are realms in which people generally have reason to allow people to choose among a variety of desires.