How the study of kata is employed in training, sparring and self defense depends on the group offering the training.
There are groups that kata is just exercise, entirely separate skills are used for sparring and yet different skills are used for self defense.
And there are many other groups.
As for sparring, I guess you're referring to some situation with rules. In those cases the type of technique tends to be that which concides with the rules in use. For example most people who engage in tournaments all use the same type of technique, and on the surface it may not seem like kata skills.
There there are those who's training encourages kata skills to be used in all sparring (ie tournament), and there are groups that practice un-restricted sparring and only allow kata technique to be used.
So it depends on a groups orientation. When I played tournaments I used tournament technique, but as my karate interestes changed I set tournament style sparring aside.
As for self defense, it is very rare an attack will match the same sequence of events that kata shows technique. More modern study of kata often gets into fractal analysis of technique, how pieces of a kata movement can stop or end an attack, and the assosciated study of how to set up those moments.
The first value of kata is that of learning technique execution within chains of movement. The second value is to learn how ot increase your power of technique within movement. These are not short studies, but then karate was never intended to be a short term study.
For example if you were one of my students you would be incorporating kata study into your training for your lifetime.
So you will find many answers, and which ones you or anyone choses to listen too depends on your personal belief, which in the end is what system of study difference hinges on.
bushi no te isshinryu