What the difference between two wraps of double density Teflon tape or
four wraps of single density Teflon tape????? If this is too technical
for the average plumber just skip it.

The only difference with single density is you'll have a better
chance of the tape getting sliced or pushed out of place. This
could cause the tape to enter the system or not seal as expected.

If you are careful to wrap clean pipe threads carefully the above will
not happen. Double density tape is required for natural gas lines as
it is more dummy proof than the white.