New fans should absolutely not watch the movies.
So much is cut out, and it's not like it's animated particularly well or anything either.
There are 3 reasons why it may be preferable to watch the movies:
*Many people like to watch anime but don't like to read manga. So if they want to get into Berserk without reading the manga then they have two options. They also prefer to watch 3 sub 2 hour movies over 24 episodes of 25 minutes each. It's an issue of time investment.
*The older anime has dated as fuck animation and a crap ton of stills because it was clearly made on a budget. And even at 24 episodes it manages to cut many parts of the manga (or in many places completely alter them) on top of neutering some graphic elements. The newer movies while heavy in CG still feature better and fluid action than the old anime. And what they show, they show in explict detail.
*Anime starts after major events have already happened. The major difference being that it doesn't show a ton of aftermath scenes that the manga does. So it's a half way between the manga and the movies in that regard... in that regard you might as well watch the movie which starts
events in chronological order and thus easier to digest (with the pay off being even more shocking if you are experiencing it for the first time).
Ideally you would want to read the manga and then watch the anime/movies. But people don't have the time for that so they are going to watch the shorter anime versions anyway. And people are going to watch what is most recent.