Yes, a slide is a positive. That is a big advantage right there, because the printer has something to try to match. With a neg the printer's opinion comes into play, because they have to imagine what the neg looks like as a positive. Some photographers prefer slides/transparencies (what they call slides bigger than 35mm) because when they submit it for reproduction (to a printer or magazine, etc...) it should get printed with the "correct" color (this is sort of hoo-ha in my opinion, but it's not worth going into).
Slides tend to have higher contrast and color saturation than prints from negs. This can be a pro or a con, depending on what you need to do. Slides are easier to scan than color negs (they don't have the orange film base to correct for). Slower ISO slide films look pretty good, but I think it usually looks worse than neg film at speeds higher than ISO 200.
Another reason to use slides is that they are very picky about exposure compared to neg film. In the printing process exposure mistakes can be corrected for with neg film. You'll spot the exposure mistakes easy with slide film. It's goo for testing and learning proper exposure. Even experienced photogs who shoot slide film often test with Polaroid film to make sure the exposure is good; especially with the larger and more expensive formats.