What's the impact of allowing other players to continue while you choose tickets?
Allowing play to continue can give the player who is choosing which tickets to pick up an advantage:


Other players may place a route blocking one of the tickets the first player was considering keeping.
Seeing what colours others pick up can indicate where they're going. Another round of this can only help decide which routes are worth keeping.
If play has gone full circle while you're deciding, you also are guaranteed to know which colours will be available for you to pick up once you've selected your tickets. This is huge.


I thought I remembered seeing advice somewhere on the site that said "always let play continue if you're choosing the tickets, never let it continue if it's someone else", but I couldn't find it. While this is certainly the most "effective" way to play, I personally think it's a bit underhand.

I prefer to play as written in the rulebook, but if it's a causal game and people want to keep playing, I'll generally let it happen (no matter who is choosing the tickets). It definitely gives an advantage to the player choosing their tickets, but it's not game breaking.