Keeping your squad happy and focused is one of the hardest tasks facing a World Cup coach, and the temptation to rotate selection to give everyone a game must be very strong. But, to me, the advantages of playing your best team whenever possible far outweigh any other consideration.
Ireland are going into action against Australia today with what Eddie O'Sullivan considers their best side. So did Scotland against Fiji early today but they didn't have much option because, unlike the other three Home Nations they still needed to qualify for the quarter-finals.
England and Wales, however, have both opted to rest most of their first-choice players. There are varied reasons for this but I believe that both camps are wasting an opportunity.
There is a difference in the Irish situation. O'Sullivan considered naming a weaker team and giving the old warhorse Keith Wood a spell out of the front line.
But that would suggest they didn't think they had a dog's chance against the Australians, and the Irish won't allow themselves to think that way.
If they win, they avoid France in the quarter-finals and meet Scotland or Fiji instead. It's a tall order but they have a chance and if they don't win, a good performance would send them forward with confidence.
It's exactly the spirit a squad should bring into the tournament. You must give yourselves a chance against anyone. Your doubts are your worst enemies.
If England have doubts, they are not about whether they can beat Uruguay tomorrow but whether the great form and sky-high morale they arrived with have been fatally damaged after lacklustre displays against South Africa and Samoa.
Their strongest side should have gone out against Uruguay in search of their lost rhythm and control. They need to play their phases and feel the ball going swiftly through hands.
Nothing in practice sessions equals match play, whoever it is against. I'm sure that Matt Dawson and Jonny Wilkinson would have particularly welcomed sorting their games out. Seeing a stream of penalties going over wouldn't have done Wilkinson any harm, either.
Once everyone looked comfortable and confident, they could have started bringing on the replacements. It is not as if any player needed a break. Unlike unfortunate countries such as Argentina, Italy and Tonga, our teams have had a week's rest between fixtures.
Wales have a totally different prospect tomorrow. Facing New Zealand wouldn't be relished by any team but I am very disappointed they are fielding what is called an "experimental team" with "development" in mind.
I can think of better occasions for experiments, and development is what you do in between World Cups not while they are going on. What were all those summer games about if not developing the team and the strategy? Scraping through to the quarter-finals in the way Wales did was a relief but it was not an achievement. And, since there have been at least eight changes for each game, there has been no chance for the team to grow together and gather momentum.
The forthcoming matches against New Zealand and England were always going to be difficult but they would have given an indication of progress.
I've nothing against the new players who have been brought into the team. In fact, I've long advocated Garan Evans being given a chance at full-back, and the 20-year-old Jonathan Thomas is an exciting prospect. And I would never deny an exciting winger like Shane Williams a chance to shine.
But for these three to face the All Blacks in their first starts in the World Cup is not doing them a favour.
I understand that Iestyn Harris and Martyn Williams have minor injuries and weren't considered but if this was a knock-out match I'd imagine they would play.
It was essential for Wales to field their best team and try to maximise their strengths. After the traumatic Pool D matches there are no high expectations so they could have gambled all on getting in among them.
There is no avoiding the fact that you must test yourself against the best. At least they could have come out with something to work on against England next week. I hope the Irish can prove what optimism and adventure can do. They'll also be playing without pressure and they could prove dangerous animals if their pack can get at the Australians.
The Aussie front five have not settled yet and if they don't perform in that department, Ireland have the backs to cause them trouble. Argentina gave them problems up front but didn't have the backs to cash in.
Ireland have much more going for them behind the scrum and we are yet to see the best of Brian O'Driscoll at this World Cup. Today would be a good time for him to show it.