Lancaster has retained the number 10 jersey for the last-eight clash, despite Scotland international Adam Hastings returning from suspension.
"Continuity played the major role," Smith told Scotland Rugby News, after naming the same backline that started the victories over Ulster and Cardiff.
"With Dan there, we've scored 11 tries in the last two games and he did really well and stepped up for more responsibility.
"Adam is fully aware that next week, or if we get through to another round we will treat team selection again with merit for what the threat is, so to have him still getting back to form after the calf injury also sustained in this period, this is an ideal opportunity."
The Glasgow head coach insists he has no worries about Connacht boss Stuart Lancaster having inside knowledge of his son's game, particularly after the pair worked together at Racing 92 last season.
Smith added: "He's been in our environment long enough for them not to have worked together for a bit.
"The decision was around the continuity factor already explained. And with Adam not having not having played since South Africa, there was no need to go off script at the moment.
"It gives Adam another chance to get another week to be ready if something happens and we need him going forward.
"It's a good opportunity for Dan also to grow and develop in a high pressure game. He started in the European Cup quarter which is an experience that he's now gained, so hopefully he'll be ready to face this challenge."
Lancaster started last month's Champions Cup quarter-final defeat to Toulon but was replaced at half-time by Hastings.
Smith, however, stressed the switch was tactical rather than a reflection on Lancaster's display.
"I never took [Lancaster] off for what he wasn't doing. It was what I was hoping Adam would add to the game in the second part because they're players with different skill sets.
"It was because we wanted to bring Adam back into the fold and that was the opportunity. From what I saw of the game at that stage, it was closely balanced and I just wanted to bring somebody with a bit of flair, which we saw from Adam in the second half, creating opportunities."
Smith also backed Lancaster to handle the pressure this weekend.
"There's no extra emotion that we have picked up from Dan this week.
"Dan is on a journey, he still needs to grow and develop and improve a lot in a lot of aspects, and he's focused on what he needs to contribute."