Slot likened Plymouth's tactics to Manchester United's under their former Dutch manager.
He said after Liverpool's fourth round exit: "Regrets? No because you never know what would happen if we played with our starters over here.
"I think during the season we have seen a few times already that this is a gameplan, a style which is difficult for our starters but also for the players who started today. So constantly long balls, second balls, long balls. It's difficult for every team.
"We had this with Manchester United earlier in the season, and it was the same, going into a low block, kicking every ball long and we played with our starters in that game.
"So today I think it showed why we used these ones today because these players need game rhythm as well in the upcoming months, they need game time and you saw today, some of these players need to be like this to be ready for the final few months of the season."
On the senior players he left out, Slot also said: "They trained yesterday and they will train tomorrow as well. Most of the things we do for a reason, we don't just do it for a reason.
"I said before, we have to play many games now, Aston Villa comes during the week, so in the last few weeks, we have played every week twice and now the upcoming weeks, every time two games.
"Therefore it is not only for them good to once in a while have a week where they only play one game, but also for the ones here today, they need the intensity of the game because you can keep training but once in a while they need a game as well and they had that against PSV, we lost and we lost as well today."