The two-time World Rugby Player of the Year came off the bench in Saturday's second Test in Auckland to spark the All Blacks attack. Barrett created the decisive try for Mark Tele'a by sprinting through a rare gap in the English defence as the hosts secured a 24-17 victory.
The Eden Park result sealed a 2-0 series win after shading the opening game 16-15 in Dunedin the previous week when Barrett had also made an impact as a replacement.
The All Blacks head to the United States for a Test against Fiji next Friday in San Diego before hosting Argentina twice at home in August, followed by two Tests against the Springboks in South Africa in September.
Robertson said he will decide on a match-by-match basis where best to play Barrett.
"I think every Test match is different. Whether it's off the bench or starting -- he's class. He can play at fly-half or full-back. He can slot straight in," Robertson told reporters.
After the match, Barrett told reporters he had 50 minutes to see where he could influence the second Test against England.
"Ultimately, when you get out there it's on pure instinct," he said.
He said he had passed on messages from the coaches to help swing the game's momentum the All Blacks way.
"To be fair, it came down to the wire."
All Blacks fly-half Damian McKenzie and full-back Stephen Perofeta both performed well against England, but Robertson sees Barrett as an attacking asset with the ability to cover both positions.
"You just know how valuable someone's ability is, to do what he did and set us up," Robertson added. "He's a hell of a leader."
Robertson is set to have more attacking options for next month's home games against Argentina.
Will Jordan, who can play wing or full-back, is on the verge of returning having been sidelined so far this year after shoulder surgery.
Jordan has scored 31 tries in 31 Tests since his 2020 debut.
Robertson said he was proud of the way the All Blacks came from behind to win both Tests against England, but insisted there is room for improvement.
"Parts of our game can be way more efficient. We'll take the wins, but we have got to be better. That's our mind set," he added.
"We have to finish our opportunities at the start, we took the pressure off and that's not part of our DNA -- we nail those normally."
