Most spinning uses are short to medium casts or vertical presentations. On 10, 20 size reels I tie directly to the spool. 30 size and above I use a backer line and tie to it. I put enough terminal line to make my normal presentations plus enough extra to retie and a little breakage. 2 or 3 reel turns above the joined knots and on the terminal line, put a piece of tape to keep the terminal line from digging into the backer. This can happen when mating two different size lines.
When you have a small birds nest on a casting reel try this. Put your thumb over the problem and gently reel in your line. Next, slowly pull line from the reel while keeping pressure on the spool with our thumb. When you reach the nest, slowly pull line from the spool while keeping pressure on the spool. Often the nest disappears with no damage to the line. If some of the nest is recovered but not all of it, do the procedure once again. If it doesn't work do it old school. Cuss, shake your fist and get out a small darning needle to pick it apart.