Umm even with tandem axles, if you have a flat or smoke a bearing you pretty much have to pull over. Yes you can chain up an axle and limp home. Have done it before, handy trick, but like said above, it's not dual is better than single or vice versa. Not too many trailers that have an option of one or the other. It's more once the trailer out grows a single axle weight, it gets another axle.
Backing ease or control is not a good reason to go one or the other either. Single axles turn easier when backing, tandems track straighter. Either one can be a plus depending on whether you're turning or backing straight. Keeping it straight is much more a function of the distance from hitch to wheels than how many wheels IMO.