Teasing has its place, of which there are those times when it is pretty much welcomed, and then there are those times when that teasing is more so done as a means to provoke another. The whole point of good teasing, though, is to test the other person in a way to understand them better, done so in a manner which is not direct, or directly confrontational, or of a too serious tone, in order to better ascertain if there is some commonality or rapport between one to another. After all, most people fear personal rejection of someone that they respect, admire, or like, and often are a bit reluctant to expose themselves for who and what they really are or how they actually feel to that other person, without first getting a better sense of where they appear to currently stand with that person, of which, their workaround to this sort of conundrum, is often some playful banter, known as teasing.
So that, teasing in personal relationships, though it does have a fair amount in common with flirting, isn't really the same; because teasing is actually more sincere in its application, because it is meant as a means to test the waters, between one to another, as contrasted to flirting, which may have more to do, with simply trying to be manipulative or to get over on another.
In a polite society, it doesn't behoove anyone to be absolutely direct all of the time, or to not take into account and of consideration the other person and their perspective, along with it also being prudent to take into deliberation the other person's status, and therefore the better part of valor, is typically to be discreet and one of the best ways to be discreet without being direct, is to tease one another. For, after all, when somebody teases another, they usually have a fair escape hatch available for them; of which, then, if the reaction by the other party is decidedly negative, they can thereby quickly state that they were, "just kidding."
Additionally, in order to get to know anybody better, some form of two-way communication, must occur, and of which, in order to continue that conversation, this so necessitates that nothing too stupid, nothing too blunt, or nothing too insulting, happens; so therefore, teasing has its necessary place, because those that tease are often able to effortlessly cross a line, that directness would typically not be able to successfully accomplish.
So too, most people, enjoy being teased, when such is done in a manner that brings out a characteristic of theirs that they like, but are heretofore been reluctant to express, themselves. In other words, teasing can be seen as a pathway of liberation for both parties, because it is a way to open up avenues that previously have been left unexplored. So then, the right type of teasing is something that is welcomed, because in its own way it helps to clarify things that were previously left unsaid, or unknown. Those then, that tease, in that good way, are those that care to know more about the other.