The attack on the last day at Cold Harbor ended up a disaster. Grant knew it and said so in his
Memoirs:
I have always regretted that the last assault at Cold Harbor was ever made. I might say the same thing of the assault of the 22d of May, 1863, at Vicksburg. At Cold Harbor no advantage whatever was gained to compensate for the heavy loss we sustained. Indeed, the advantages, other than those of relative losses, were on the Confederate side. Before that, the Army of Northern Virginia seemed to have acquired a wholesome regard for the courage, endurance, and soldierly qualities generally of the Army of the Potomac. They no longer wanted to fight them “one Confederate to five Yanks.” Indeed, they seemed to have given up any idea of gaining any advantage of their antagonist in the open field. They had come to much prefer breastworks in their front to the Army of the Potomac. This charge seemed to revive their hopes temporarily; but it was of short duration. The effect upon the Army of the Potomac was the reverse. When we reached the James River, however, all effects of the battle of Cold Harbor seemed to have disappeared.
The recovery period for the AoP Grant gives is probably overstated. Certainly the AoP doesn't look too eager to attack entrenchments on the first day or two at Petersburg.
The part that gets forgotten is that the point of the entire Cold Harbor operation (a Meade plan, BTW) was to get around Lee's right flank, and it almost worked. Start about May 31st, with Sheridan at Old Cold Harbor and Smith on his way to Cold Harbor. If the ball had bounced the right way for the Union in the next 48 hours, Meade would have had the AoP south of Lee and closer to Richmond, on an open road with Sheridan's cavalry available to exploit the opening.
There are a bunch of reasons that didn't work out. Chief among them would be excellent Confederate performances and outstanding personal leadership by Robert E. Lee combined with some sub-par work by Smith's troops and logistical failures on the Union side. After a month of campaigning, the AoP looked a bit ragged. When Meade tried to bring his right around to his left and launch a sledgehammer blow, delays cropped up. The final attack at Cold Harbor was originally ordered for about 36 hours earlier than it actually went in. The ANV made excellent use of the extra time, preparing the defense that stopped the AoP dead in its tracks. Just as Grant said, it should have been cancelled as the delays mounted. That is easier said in hindsight than done in the midst of determined efforts to follow orders.
This was a good, workable plan that had promise of great success, but fell short because of a failure to execute. It ends with the assault of June 3rd that should have been cancelled, but was not. The failure to recognize that need is where the disaster begins.