You can use a sample to act as an instrument or as an accessory to another song. If you find a song you want to play and you think police sirens or air horns would be a great addition, you've just created a sample. Producers “rummaged through vinyl boxes for hours on end trying to find the most unique sounds to sample. Often, samples are overlapped, equalized, accelerated, slowed down, played in a loop, and manipulated to a point where the resemblance may not even be noticed.
So why add DJ samples that have been overused since we first heard about them? As a DJ, you should always strive to be original, and one way to do that is to use original DJ samples that you created yourself and use them as needed. Trust me, if you spend so much time listening to other DJs like me, and you should also, as part of improving your skills, you'll see the merit of taking the time to create your own DJ samples. There's no right or wrong way to sample, and the best way is to experiment and find something that works well with your workflow. Now that you know all the different options, where can you find them? With countless sounds to try, there are so many other places to look for them.
Either you're guilty of it or you've had the unfortunate opportunity to be present while another DJ has decided to show the public to death. Learn to use these samples the right way and your set will be better. Exaggerate and risk discouraging the crowd. If you're going to sample vinyl, remember that you'll need a record player and an audio interface to record them on your computer with your favorite digital audio workstation (DAW).
Whether it's because they haven't smoothed out the transitions or because they haven't learned the art of mixing a perfect sample, sample overload can ruin an otherwise decent set.