Cons - it's illegal in some states
Although a majority of the states allow for trailer widths of up to 8'6" there are still roads and states that limit it to 8'. I know that Arizona, New Mexico and Texas fall into this category. I could get away with not worrying about Texas but Arizona and NM would be an issue.
That being said, I really don't want a trailer much wider than 8' and even that is too wide IMHO. If the goal is for some extra space for rigging, I've got a few ideas that still allow for a temporary wider trailer when doing this but for travel is well under the 8' width limit.