When he's fit, he's the most destructive and effective wing in world rugby. He is the only player in the past 20 years worthy of comparison with the late Jonah Lomu.
But Savea can't be relied on to get or keep himself fit. Left to his own devices, the desire to stay on top of his diet and training isn't always there.
Maybe 20 years ago, players could get away with not being in top shape. Not now.
There is data pouring out of the players' jerseys from GPS packs, endless testing and measuring, and conditioning coaches who can take one glance at a player and see all they need.
In the old days, players turned up at pre-season to start getting fit. Now, players are expected to turn up fit and use pre-season to get fitter. They are also expected to view organised team training as the bare minimum and to work on an individual programme.
When they have time off - are being rested for a week - that should be read as they are not playing, but still training.
This culture of pushing the fitness boundaries is why the New Zealand derbies so far this year have been played at a frightening pace.
Even a few years ago, games in the opening round would be all blood and thunder for 50 minutes before the players began to wilt.
This year, the opening game between the Blues and Highlanders didn't flinch, leading Blues coach Tana Umaga to joke about the difference between now and his playing days at the dawn of professionalism.
"We were just as fit. No ... it is other world [now].
"When you have seen the amount of work these guys do and the work the strength and conditioning coaches put in and the hours that they do, no it doesn't surprise me [that they are as fit as they are]."
His counterpart, Jamie Joseph, echoed that view. "The demands physically on the game, on the players, are getting higher every year.
"I was actually disappointed personally as I thought we looked a bit tired in the forward pack."
It's a simple truth that if players lag their peers in terms of basic fitness, they won't be able to have the desired impact.
That was Savea's problem last year during Super Rugby.
By his own admission, he didn't work hard enough or eat well enough. He lacked the self-discipline to stay on top of two crucial aspects of his preparation.
The noises coming out of Wellington are that the same thing has happened again - he didn't train hard enough in the off-season and, without the aerobic base, isn't as effective as he needs to be and can't find the burning acceleration to combine with his raw power to leave defenders helpless.
"You are always disappointed when people come back and they are not in their best nick," All Blacks coach Steve Hansen told Newstalk ZB.
"There may be a valid reason for that. He may have been injured, or may not have been, but we know Julian has in the past had issues and the best way to deal with those issues is to take him out of playing and give him the work that he needs to bring him back up.
"I think they have a bye after the [Kings] game so I think it's a smart play. He can work really hard without having to play on Saturday and be fatigued when he plays.
"If he works really hard in the next couple of weeks, I'm sure we will see a big improvement."
Savea is the highest profile example but by no means the only one. In 2014, Charlie Faumuina was dropped by the All Blacks. There was no sugar coating from Hansen, who said the Blues prop hadn't scrummaged well enough and wasn't fit enough.
There were no complaints from Faumuina. He knew his form, or lack of, was directly linked to the fact he hadn't worked as hard as his peers.
Look at him now. He's in the form of his life, as he was at the World Cup, and it's all because he has found the self-discipline to eat sensibly and use his time more wisely to fit in more training.
His team-mate Steven Luatua suffered the same indignity of being singled out by Hansen in 2014. Not fit enough, said the coach, and, two years on, it's an episode Luatua still carries with him.
He's looking like the player he was in 2013 and that's down to one reason: he has found self-discipline. Now he is prepared to work at least as hard as the next guy, if not harder.
Maybe the biggest improver of all is Joe Moody - who made it to the All Blacks in 2014 without the country knowing who he was, only to be underwhelming once there.
There was an initial sense of dread when Moody was called up to the World Cup squad ahead of the quarter-final and almost panic when he had to be injected into the fray after half an hour.
But he was a revelation, not just on the night but also for the next two games, and has only got better since he returned to Super Rugby. The difference, as Hansen pointed out at the World Cup, is conditioning. "I think fitness has probably been his biggest handicap, or lack of it. He's one of the strongest guys in the team and he can play rugby, but the limiting factor is how long he can play for because he hasn't been fit enough.
"He has turned up in magnificent condition and he has got the reward for it. He scrummed well, he played well, did his job at the lineout and carried. Those skills go when you don't have the ability to get to the right places because you are not fit enough."
Self-discipline is everything now. Those who don't push themselves don't get the rewards.
