E-Prime certainly helps you say things without unwarrented certainty, and without sounding weak and without having to add caveats and conditions. I find I can express lack of certainty in a possitive way rather than as a sequence of negatives. Of course, some people find it hard to function without black and white thinking and find E-Prime statements non-commital, but they would also find any expression of uncertainty difficult, especially when phrased as negatives.