It depends on the film, and on the trailer.
Sometimes getting to see snippets gets me excited. Sometimes it warns me not to bother. All too often it gives away too much.
I even once kept seeing trailers for a movie for so long I got sick and tired of the movie before it even came out. (Surf's Up)
(My 'favourite' is an old Foxtel trailer for A Christmas Carol with Patrick Stewart, that literally tells every single plot point from beginning to end, even talking about Scrooge's turn-around in the final scenes. I came away thinking, 'Most people know that story already; why do they need it retold like that? And the ones who don't... way to spoil it, trailer!' I couldn't find said trailer on YouTube.)

But there have been very good, very atmospheric trailers that have made me want to watch things that would never have been on my radar. One like the GotG trailer tells me we're getting close to it getting released. So, yeah, for me some are good.

The Dancing Baby isn't an Ally McBeal thing; it was an early internet vid. (AFAIK; I've never seen Ally McBeal either. Nor Single Female Lawyer.)

~ Le Messor
"I wish I knew as much about anything today as I knew about everything when I was twenty."
~ Bill Ayers