I personally don't use many samples, usually only for percussion and single-shot type sounds. Any melody, I prefer to create myself. The only reasons why I usually don't sample much is because I'm honestly just too lazy to search, too dis-organized in the fashion of how I organize my samples, and lazy as well to edit them. Also lets say I use a sampled Piano loop, guitar loop or similiar sampled melody, I have a hard time adding in my own sounds and making it all fit right with the sampled melody.
The thing I do like about samples though is that it usually gives your beat a raw, dirty, dusty, sound. I love that lo-fi sound you hear in a lot of older beats, vinyl dust,etc... It just gives that imperfect sound which is great for hiphop. I also don't mind hearing samples that ain't looped perfectly, the ones that have a little gap or cutoff space before it loops, just because it adds that imperfection to the sample.
What I really want to start doing though is sampling drumbeats, then just flip them around to my likings. Reason being, so I can get that dirty more acoustic sound and so all my percussion sounds nicely glued together which I have a hard time doing with single-shot sounds. It's kind of hard to find drumbeats just by themselves though, usually there's a bassline over them or something else.