Well yes and no. In the 'no' case it would be in order to allow the fewest possible side-effects to the intent of the script (say in a situation where dialogs are called sequentially to elicit more than a single string from the user to determine the eventual flow of the script).
But here's what I think you mean by a 'yes' case. Let's call our apps Sender, Target, and Interloper.
Sender is filling out a form in Target which has 20 fields in it but it only requires 2 strings from the user to auto-complete the fields. Sender sends this script to Target.
try
tell application "Target"
-- dd#1
set field "UnixUserName" of form 1 to text returned of (display dialog "AppleScript Team member name:" default answer "chris")
end tell
my AutoCompleteUserFields() -- targets another app and gets some input values on idle
tell application "Target"
-- dd#2
set psize to text returned of (display dialog "Page size:" default answer "8.5x11")
end tell
my AutoCompletePageFormat(psize)
my ProcessPrintJobFolderFromCurrentForm()
end try
Now the script is running and paused at dd#1 but Interloper has a script aimed at Target which it sends on startup. Guess what? It's being run from a cron job and activates while the user is typing into dd#1 with the intent to fill out field "UnixUserName". Because the 'yes' behavior permits interaction, then before AutoCompleteUserFields() is called, field "UnixUserName" will be filled out with potentially incorrect information. And even if that event couldn't get there before AutoCompleteUserFields(), it sure will on Sender's idle handler. Now it's easy to see that I could reformat the script above to try to insure my values are correct, but I think the point is that Sender's idle handler permits Interloper to access Target and thus a potential interceptions of the script's intent. That's what folks want to avoid because there are other possible scenarios where you'd be using values from say Target's application properties and want them to be reliably set for the duration of the script.
Judging by the comments of other posters to this question, the sentiment is certainly against other application interaction -- or even the perception of it.