I use Loctite's pliobond adhesive for knots. I used to use CA, but decided to try some a bit more flexible: Loctite Vinyl, Fabric & Plastic Flexible Adhesive from Loctite Adhesives
I apply my thread and whip finish, and then rub some of the flexible stuff into the thread. I've never had a thread come undone, and it will migrate below the surface of the thread. The package says 30 minutes, but it's been my experience that it's tack-free in a couple of minutes, especially if you squeeze it into the thread. This is for making loops in the leader end of lines.
For smoothing out knots, I would use one of the flexible adhesives. CA is hard, and won't bend around the rod's tip like a flexible adhesive does (or does better at least). The Loctite stuff is available at Lowes, and sells for aroudn $3.50. I've had the same tube for over 18 months, and it's still nice very fresh.
I've not used any of those, but have used a CA glue on knots just to make them smoother, so they catch on grass & debris less. I use Pro's Plastic Bait glue, since I usually have a bottle of it anyway, and it stays flexible. However, I don't use glue on knots to improve the knot strength, I feel if I tie them correctly to begin with it's not needed.
The only issue I can think of with using any type adhesive, would be does the solvent in it damage the line material? If so, you're really not gaining anything by using it. CA glues do not as far as I can tell.
Within the realm of the 'always trying something new' world of fly fishing I am not exactly a trend setter. I've never glued a knot, practice led me to being able to create neat, small, and strong connections at all points of my lines. Perhaps glue does make them stronger, maybe smoother, but I believe that we as fishermen are over thinking many aspects of the game. For some the research an study of the seemingly infinite possibilities that one can pursue is a most enjoyable aspect of anything they undertake. I have fallen into this group but my association has been along the lines of how to catch more fish and not so much into the mechanics or physics of our terminal tackle.
After having said that I will add that if applying a glue to your connections gives you a sense of better engineering as far as the knots are concerned, then I think you should do it. As far as believing myself that I have ever had a failure because I had not coated a knot with something; I have never given this a thought and don't believe it ever happened. When it comes to setting up gear; it's your gear and you should do whatever you feel will be an asset.
I think the OP isn't trying to strengthen his knots with glue, just trying to make a smooth transition that passes through the tip easily. Dave Whitlock's Zap-a-Gap line to leader connection is one solution, and I used that for a couple of years with very good results. I also used the same connection for line to backing, but my backing doesn't come into play very often. A nail knot isn't really bad, but they can get hung up a bit on the tip, and I've known people who use a bit of Pliobond to smooth that out. A needle nail knot is a bit smoother, and I used that connection for a couple of years as well. My current method is is a loop to loop line to leader connection. Factory welded loops fail, and it's not uncommon to make one's own loop. I prefer my own loops over the factory loops, and use tying thread to secure the loop. I use Loctite's thin flexible adhesive to very lightly coat the thread. It seals out water, and prevents any fraying of the 6/0 thread I use. I've used the same loop for hundreds of hours without failure, and managed to keep the thread wraps to a bare minimum: two or three layers over a 1/4" length.
P.S. I tie my leaders with blood knots, and have heard some people say that they use Pliobond to smooth out the knots. My knots have never presented a problem for me, so I don't do that. Seems like too much trouble in any case, and I can be lazy.
I've used them all and do favor Zap a Gap or Knot Sense and like Franks said not so much for added strength, except on GSP where it stops slippage, but rather for making a super smooth connection that doesn't catch on weeds.
I was going to use it to smooth out knots so they dont catch grass and such. Im pretty confident in my knot tying , just wanted to neaten things up a bit. I'll have to pick up some zap a gap on my next trip to BPS.
I used to use shoo-goo to smooth knots, particularly the flyline to leader knot, so they'd go through the guides easier. I had an old tube that was cracked and drying out. It was easy to ball up a bit of it and mold it around the knot and it dried quickly and stayed flexible. I did it cause I read somewhere it was a good idea. The plio-bond took several layers and took a long time to dry. Eventually, I quit messing with it cause I didn't seem to need it.
I have a new bass taper that I'll get to try out this summer and a lot of that will be in weedy ponds. I may go to a slimmer knot/transition and straight level mono and some smoothing may be in order for that rig.
I have found that super glues like Zap a Gap are too rigid to use on fishing line. I used to use Zap a Gap to secure loop connectors on the ends of fly lines, but the lines eventually developed a weak hinge right where the rigid glue ended. You need a flexible glue that will flex along with the line as it bends and turns over. Now I use Pliobond and have had no problems.