What do the true and false booleans means in .spawn

Hi, i'm trying to do some JS validation to make certain page templates hidden and visible based on dropdown menu options, and in all the threads and forums I see people using .spawn but with variations on the true and false booleans that come after it. What do the true and false mean/do/signify?

For example: in this statement what would the true and false be doing?

else if (event.value=="2") t3.spawn(false, false);