For example: Alien: Covenant had fewer trailers and more shorts introducing the characters or updating us on the events following Prometheus, while Spider-Man: Homecoming just had many, many trailers.
The upside of shorrts: It delivers original content, provides more depth and can bring in new moviegoers who are invested after getting what is essentially a spoiler-free taster.
The downside of shorts: at times it means you have to watch them to fully understand events in a film, as Covenant taught me the hard way.
Upside of trailers: Moviegoers can get hyped over something in a movie (as I did when Michael Keaton turned up in Spider-Man's trailers as Vulture) and show off some of the set-pieces in a movie.
Downside: Way too many spoilers usually get dropped and you're seeing 4-5 minutes of footage of something you'll enjoy even more when seeing it for the first time. Trailers can genuinely ruin movies and it's a damn shame when they do.
In my opinion: A mix of both really helps, especially if trailers are essentially spoiler-free. I'd obviously choose to see original content over something I'm going to pay to see again, but with context. On the verge of cutting myself from trailers entirely with how much they give away nowadays, but with trailers like Black Panther I can't help myself.