One of the great qualities of this BB is that these topics often go off on different tracks. So allow me...

DT posited that Vito sent Luca off to meet with the Tattaglia Family "for no good reason." I think that there was a tactical reason as Vito rarely too any action without a purpose. I think that Vito miscalcuated the entire Sollozzo proposition, including sending Luca to infiltrate. But had it worked and Luca struck Sollozzo down or been an effective spy, then it would have been a brilliant tactical move for the Corleone Family. Such a mole would have given the Corleone's even more power.

I know this is a pet peeve of DT, but allow my explanation to reference the novel. When Hagen told Vito that they would have to grant Sollozzo a meeting request, Vito stated that "now that the wedding will be over, set it for anytime you like." The answer told Hagen that the answer would be "no" to Sollozzo and that Vito expected the "no" to cause problems (which it did). Hagen also privately felt that Vito was wrong to decline the drug proposition and that it was one of the few times that Vito's judgment was flawed.