The debate is in full swing over whether Dan Biggar should start for Wales against Scotland on 9 March after his outstanding 20-minute cameo in the 21-13 Six Nations win against England.
The Northampton Saints fly-half came on in place of Gareth Anscombe after an hour with Wales trailing by a point.
His contribution included a remarkable 60-metre clearance kick under pressure, one brilliant take under an attacking high ball and outstanding assists in both Wales tries. Oh, and a touchline conversion.
Biggar's was a key intervention in a superb team performance, without doubt.
So as Wales set sights on Scotland en route to a potential Grand Slam the arguments have started about who will wear number 10 in Murrayfield.
It would be the same if Wales were sliding in the direction of a wooden spoon - this subject eclipses Brexit over breakfast on the western side of Offa's Dyke.
But should there even be a debate about who starts if the strategy of starting with the runner Anscombe and finishing with the cool-headed Biggar is working so well?
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After all, Wales have won 12 consecutive matches and, if it isn't broken, why mend it?
Biggar has come off the bench in Wales' wins over Australia, South Africa, France and England in the 2018-19 season
In what is effectively a 23-a-side match over 80 minutes, substitutions are commonplace and, as Biggar's display shows, can be key to the outcome of a tight Test match.
But the ex-Ospreys player's performance will go down as one of the great substitute performances in international rugby.
Here are four others to savour.
England 28-17 Wales, 2003 Rugby World Cup
Mike Catt was a late addition to England's squad at the 2003 World Cup in Australia.
At half-time in the quarter-final against Wales in Brisbane, England coach Clive Woodward (pre-knighthood) was glad he had the South African-born midfield man in his arsenal.
Wales were leading 10-3 and England's talisman Jonny Wilkinson was off-key at fly-half.
Catt came on for wing Dan Luger but spent most of his time standing at inside centre alongside Wilkinson, sharing the tactical kicking duties.
With Wales suddenly having more than one midfield playmaker to nullify, Wilkinson resumed his usual service, kicking England to victory despite their opponents outscoring them three tries to one.
Two games later he did the same thing as England lifted the Webb Ellis trophy, but for many the World Cup was won at half-time in the quarter-final by Woodward's quick action in getting Catt on the field to support his star fly-half.
Ray 'Chico' Hopkins
England 13-17 Wales, 1970 Five Nations Championship
Gareth Edwards was an immovable object in Wales' number nine shirt between 1967 and 1978.
So imagine being Ray Hopkins, a hugely-talented scrum-half, in competition for international selection with the man who would later be voted the greatest rugby union player of all time.
In 1970, replacements during matches were allowed only for injured players, so there was no emptying the bench in the last quarter. If players were fit, they stayed on the pitch - even if they were having a stinker.
Hopkins' chance came when Edwards limped off in Twickenham with 15 minutes to go and Wales trailing.
The Maesteg man made a try for JPR Williams and then scored one himself as Wales triumphed.
Edwards never again failed to finish a game for Wales, and Hopkins didn't play for Wales again. But he did make a Test appearance off the bench - again replacing Edwards - for the British and Irish Lions in 1971.
Frustrated by his lack of international chances, Hopkins went north to play Rugby League.
But as two-match international careers go, his was probably the best. A win over England at Twickenham and a victory against the All Blacks in Dunedin.
Ireland 24-7 France, 2015 Rugby World Cup
Ireland needed a steady hand at fly-half when Johnny Sexton limped out of this crucial pool match in Cardiff.
The winners would avoid tournament favourites New Zealand in the quarter-finals and open up a potentially easier route to the semi-finals against Argentina.
Sexton left the field midway through the first half and captain Paul O'Connell was carried off with a career-ending leg injury before the interval.
With big boots to fill, Madigan kicked two penalties, a conversion and successfully unleashed Robbie Henshaw as an effective attacking weapon.
According to the BBC report of the match: "Madigan produced a tremendous display after his introduction as he conclusively won his battle with France fly-half Frederic Michalak."
Can't say fairer than that.
France 20-18 New Zealand, 2007 Rugby World Cup
Michalak had his own super-sub performance in the Welsh capital as France caused the biggest shock in the history of the World Cup, until Japan overturned South Africa in the 2015 tournament.
Favourites didn't come any hotter than the All Blacks. A 40-0 win over Scotland was their narrowest in four pool matches.
But on a remarkable night in Cardiff, France had an unyielding defensive plan and a not-so-secret weapon on the bench in the shape of the mercurial Michalak.
They made almost 200 tackles as the All Blacks spilled the ball, put their feet in touch at crucial moments and struggled with referee Wayne Barnes' interpretation of the tackle area.
And in the second half France - through Michalak - struck.
Damien Traille fed the fly-half, whose burst of speed took him away from the chasing New Zealand players before he off-loaded to Yannick Jauzion to touch down.
Jean-Baptiste Elissalde's conversion put France on top and, inspiring comparisons with their legendary 1999 semi-final win over the All Blacks, they held on for a famous win.
How big a deal was this? Well, put it this way, New Zealand have not lost a pool match or a knockout game in the World Cup since.