I am not one who subscribes to the idea that fish know what line is if they see it, so makes no difference if I use mono or fluoro. Line laying on the surface can cast a shadow which may spook some fish, but it won't matter what type of line it is!
I use braid on some of my baitcasters, and often tie direct to lures, no leaders at all, and still catch fish! I'm sure they can see the line, but their pea brains don't seem to know any different!
However, I do use fluoro for tippet material sometimes because as zug buggin has said, it sinks. I usually buy Triple Fish brand fluoro when I buy straight fluoro. It's not "tippet" material! I also make my own leaders, and use Yozuri Hybrid, which is a fluoro coated, mono core line. I get the advantage of fluoro, it sinks too, but it's not as expensive as straight fluoro. I also use the same line on some of my bait casters & spinning reels, so I don't have to buy a lot of different lines. I've connected straight fluoro to mono many times, and agree with Ard, a good knot is a good knot, and I also use a blood knot most of the time. I will also use a surgeons knot with very light tippets and have had no problems even with fluoro.
I haven't bought "tippet" material in many, many years. It's not necessary, particularly for subsurface applications.