Leaders

One other point regarding the above, a sharp "tug" will remove coiling
from line that has not had its shape ( New line for instance) for very
long. But is also shock loads the line, and is not a good idea in fine
tippet. Fine nylon will be compromised by this.

Most especially if you do this with fluorocarbon tippet for instance,
it causes stress faults at the point where you held the line while
tugging it, actually increasing the memory at these points, and on
coated lines it can compromise the coating, which in turn compromises
the knot strength.

The main advantages of heating the line in water, is that no shock
loading takes place, it is not stretched, and no particular point on
the line is subjected to specific thermal or other stress.

TL
MC