It is always essential but even most when the farm is not empty after the external team gets away. For instance vaccination of departure of half of the flock to slaughter-house.
To have these teams aware of best practices, farmers should first offer good facilities to them: enough space, clean areas, visible barriers, hot water to wash hands or shower…
Then clear big boards with pictures would help with implementation of best practices.
And all these teams should be supervised and regularly trained by vets who should organise the collection of farms specific biosecurity measures to prepare the teams.