Sometimes it is necessary to ambiguate things. The bottom line is that I don't lie.
Say, I have DOG. I don't want my neighbor to realize that I have only one dog, because if she realizes that I only have one, she will call me to find a partner for it, which I don't want, but I also don't want others to know that I have more than one dog, because some people may ask me to pay more charge for the town. If in the situation, people ask me a question: "What pets do you have?" I don't lie and don't want them to know wether I only have one dog or more dogs. I just have DOG generally. What could I say?
As for the gender of people, I don't want the listener to know if my friend is a girl or a boy, because if I use the pronoun "she" in the later context, the listener may say: "Oh, you have a girl friend now!" which I don't want to discuss about. If I use "he", the listener will advice me to make girl friend, which I also don't want to hear. I just want to express the concept of 3.SG.
Maybe the examples are not so realistic, but I often find it burdensome and awkward to have to meet up the mandatary grammatical requirements in a language in a conversation, because I sometimes want to avoid to expose wether something I only have one, or have not only one, and a friend which I have is a boy or girl. Besides, considering about politeness, I should also pay attention to these.
There are some mechanisms that are used for that, while not all of them are suitable. One of the largest problems is that it can works unnaturally. If I say "I like dog or dogs. Now I have a dog or some dogs, I am happy with it or them, but it or they eat so much." It is also unnaturally to say: "I have a new friend. The friend is very nice and helpful. Whenever I have questions, the friend explain to me in detail. Tonight I am going to dinner with the friend." Here I have mentioned "the friend" several times, which is very weird, and the listener would suspect that I am trying to conceal the gender of the friend. Furthermore, some written forms cannot be adapted to oral language. We do write "she/he", "(s)he" and so on, but at least in daily conversation, the forms are uncommon.