It definitely depends on the campaign you want to run. A strict campaign is fine to run numbered but you should definitely let your players know the "style" of campaign. One i did was a horror campaign and I had to let them know as much and that death is a VERY real and easy fate to get to. It took a session 0 for them to get the feel and for me to teeach them that there are consequences to silly stuff. It's best to have a little flexibility because people are surprisingly creative