The great majority of Bridge players use the strength discard against
a trump declaration, and there is little doubt that this is sound.
It is imperative that you protect honours in the weaker suits, for
rarely will your long suit be brought in against the dealer.
The claim made by those who use the weak discard against a trump
make is that it permits them to throw away a short suit, and thus
eventually to establish a “ruff.” When a player is discarding from
strength, this “ruff” can be obtained with equal facility by the
proper use of the reverse discard.
Without a doubt the weak discard should be used on a spade
declaration that has been doubled either by you or your partner. In
this case, trump strength is probably with you, not against you. The
same argument cannot be used, however, on a doubled heart, diamond,
or club, whereas spades may have been declared from weakness, the
other declarations indicate trump strength.