It means that McClellan and the Army of the Potomac can use the James River as a transport and supply route during the Peninsular Campaign, rather than the less convenient York River. This radically changes the strategic situation in the summer of 1862 and makes it more likely that Richmond will fall.
This is nonsensical.
Norfolk was occupied by the Union on 10 May;
Virginia was scuttled on 11 May, and the surviving elements of the CSN's James River Squadron retreated from the broad tidal estuary of the lower James past Drewry's Bluff to Richmond. Thereafter the Union was free to use the James as a supply route.
At about this time, the Army of the Potomac had driven back the Confederate rear guards at Williamsburg, and advanced to West Point, at the Pamunkey and Mattapony join to form the York. The southern flank of the AotP was on the Chickahominy River, which runs between the Pamunkey/York and the James and turnd south into the James. During this advance the AotP ignored the area south of the Chickahominy.
The AotP's supply base moved up to West Point, because it was the nearest port, and there was a railroad leading from there to Richmond. McClellan planned to use this railroad to move up superheavy siege guns with which to breach the defenses of Richmond.
Meanwhile, he shifted most of his army south of the Chickahominy to approach Richmond from due east.
Then on 26-27 June, Lee attacked the remaining Union corps north of the Chickahominy and cut the supply line to the Pamunkey. McClellan then retreated southeast to the James, establishing a new supply base there, at Harrison's Landing. The AotP remained at Harrison's Landing from 1 July until August, supplied via the James with no Confederate interference. McClellan however was thoroughly beaten in his own mind and there was no chance of Richmond falling in summer 1862.