Sam sub meh.. I dunno about it. I wanted to level it for a sub. But even then I never wanted to use it in an exp party. In my opinion sam sub is basically for show.. perhaps for farming, but really the only thing you get out of it is a bit faster TP gain. Which you might be wondering, what could possibly be wrong with that..
Well, doing multiple heavy damaging weapon skills is going to make it incredibly hard for your tank to do his job. You're going to get aggro.. and perhaps even die. As far as I see it sam sub is just for show. That's all ive got to say about that.
As for why a drk would want to sub thf at all, that's simple. Granted, in my opinion subbing thf before you get Trick Attack is pointless, and if you arent aware, that is any level before 60. Up untill this point /war is the far better sub to use. However, at 60 Drks get two new WS's to play with: Guillotine and Sickle Moon. Guillotine is a godsend compared to every scythe WS up to that point. Dealing easily anywhere from 200-900 damage without using Souleater + Last resort. With Souleater + Last Resort it can and generally does do 900-1000+. So far I believe my highest hit has been 1500something. Honestly though I do not believe Guillotine even combined with last resort and soul eater can do that high of a damaging hit without the help of sneak attack.
Why then you ask we use trick attack? Simple really, after doing such a hard hit with SaTa + Soul Eater + Last Resort +Guillotine, I even as an Elvaan am left in a severly weakened state with roughly half my HP (or more) gone. If that WS wasn't used as a killing blow.. which it generally isnt because you want it MB'd off of, without Trick attacking onto someone your risking immenant death. Half HP and a mob that wants to kill you is what you get after that, it's not exactly ideal or healthy for that matter.
Trick Attacking onto a tank (or a wandering whm

) garentee's we're safe, and even though we just took a huge HP loss, the healer will be able to heal us easy enough while the tank goes about his/her buisness as usual.
The thing about guillotine is without Sneak Attack it's damage output is very sperratic. It may do 936 dmg one time and it might just do 283 dmg the next time, and then do 628 dmg the next.. it's not a hugely reliable WS without some kind of modifier and in this case Sneak Attack pretty much garentee's it's going to hit for at very least 600-1000, the higher end of the spectrum.
As far as Sickle Moon goes, it's no Guillotine, but for GS it easily the most damaging weapon skill up to that point, while generally it tends to dish out 200-600 damage on normal Sneak Attack hits, but (for me) It can do up to 700-1000 damage after a Last resort + souleater + SaTa hit. Without the use of Sneak Attack it too has a slightly sperratic damage output and only tends to do 200-500 dmg, and rarely sometimes doing something over that amount.
I love subbing War, lets me just go all out. TP gains are much faster, but its highly risky and when you go all out.. you're pretty much signing a death warrant. Where as subbing Thf lets you go all out with safety.. not to mention you can take over Thf spots in Nin or Pld parties (though really.. by 60 Pld's shouldnt be having trouble holding hate unless theres a really gung-ho Rng in the party.
Oh.. and that's another thing.. I <3 rangers now.. instead of loathing the fact that can do dish out the uber damage so much faster and earlier than us.. >.> (*breath*) With a ranger in the party we're bound to produce some kick ass xp per hour paired together. Slug Shot/Side Winder >> Guillotine 4tw. ^^