One of the main factors is durability, casting day in day out thin line wears out, 60 and 100ilb JB is amazing braid and lasts for a long long time, if you get a bad section in the braid then splice a new section on, do not throw away the rest of the line, splicing is easy as Josh W says. We use it for top water, jigging and backing on all our game reels, making small wind on leaders and end connections on our saltwater fly lines, 60 and 100lb covers everything but its also nice to have a bit of 130lb JB lying around so you can splice it into the 60 or 100lb braid if you want to use a 130lb topshot.
Here is a little trick for you, when splicing mono into the braid, instead of whippng the end down with waxed floss or braid use the tag end of the 60 or 100, do one half hitch with tag end on the mono then do alternate half hitches back down the braid pulling tight (about 8) then finish off the knot with a finishing knot as you would do with a bimini twist, rub some glue into the knot and done, will last for a long time, small compact knot (about 10mm long). We use this on finishing our splices on our backing to our game reels, and connections on our fly lines and where ever we splice mono into 100lb braid or less, been using it on our fly lines for a while now and have not had to replace a connection splice due to this failing and that says a lot if you saw my casting