when i troll, i use a 4 ft fluoro carbon leader with the crosslock snap and the barrel swivel junction. this makes replacing the leader easier, imo. while trolling you dont really cast much(just to reset after you catch one). anything longer than 4 feet seems silly to me up there, the fishing pressure is so low that as long as you dont have a super obnoxious line right on the lure you should be fine, but, my brother uses fireline crystal (looks like dental floss in the water) a big white line right to the hooks and catches enough fish, so who knows. when i go to cast i simply snip off the knicked up 2 feet or so and have a 12-18" leader of flouro for casting. the barrel swivel junction is something ive used while tipup fishing for years prior to using braids on a bait caster so it just seemed logical to use that approach.

i think there are multiple advantages of using a braid up there over a full spool of mono but most are my personal beliefs.
1. on a baitcaster- if you ever get backlashes with braid they are easy to get out and dont kink your line creating weak spots
2. if you do break off, you only lose the leader portion and dont lose large chunks of line leaving you short spooled
3. on a baitcaster-i like the feel of braid on my thumb for casting over mono
4. on a baitcaster-my reels are spooled with braid year round so i dont have to change-im lazy
5. on a baitcaster-i like the braid because it has ZERO memory, mono/fluoro still have a tiny bit and i find it casts better with braid
6. sensitivity, you can see what your lure is doing on braid. you sort of can on mono, but with braid you can tell the difference between rocks/gravel/sand/mud bottoms if you are hitting bottom