I was a USGA Committeeman and rules official for 13 years. In one of the first events I worked, I was giving a player a red hazard drop, which would have put him right on a cart path. I "skipped" that step and took him to the other side of the path and dropped his ball there. The senior rules official was observing me from the top of a hill a few hundred yards away. After the player finished the hole, the senior rules official came to me and asked me about the ruling, which I went through with him. He said (and I never forgot this)..."why didn't you drop his ball on the cart path?". I said, "because the path is an obstruction and he would be entitled to relief from it". He told me to NEVER skip a step. He explained that (a) I don't know where the ball will go after it is dropped, and (b) the player may prefer to play it off the path, which would be his right after taking a hazard drop. On that day, I learned the importance of taking each ruling one step at a time.
What Spieth did was brilliant (and it made Johnny Miller look like an idiot for insisting that his best deal was to go back to the tee). Spieth knew all of his options. He stood on the top of that hill, with John Paramor to get confirmation that the spot where the truck was parked was on the line backward from the flagstick to his ball (it was). He knew he had the right to drop behind the truck (on the proper line). Recall that he didn't drop behind the last truck, he dropped in between trucks...this was also very smart and took 10-15 yards off the shot he ultimately played. He then knew he'd get T.I.O. (temporary immovable obstruction) relief from the trucks. From there, he could drop it on closely mown grass, about 230 yards from the green, where he had a chance to hit it close to the green (which he did, but he could not have from the tee of a 505 yard par 4 Johnny Miller!). From that spot, he got it up and down for an all world bogey. Agree that it took too long. Disagree that he did anything improper. Sometimes it takes awhile to get the rules sorted out. I felt sorry for Kuchar for his wait. I was VERY IMPRESSED with Spieth's poise under pressure and his knowledge of the rules of golf.
TS