I used to have enough fear of marginal VFR conditions that I would never embark on a trip without perfect 10-mile visibility and stable cloud layers more than 4,000 feet agl. That was probably a great personal minimum for a brand-new private pilot but is ultimately unrealistic for someone wanting to go farther. Unless a trip happens to fall into one of those rare, “severe clear” high-pressure systems dominating most of the nation, odds are that somewhere on a long cross-country trip, marginal conditions will exist.
Source: aopaVFR Unleashed: Are we allowed to do that?