The tribal heads had been sent on what's now called a pilot trip, to stake out, choose the best location for the tribe to settle once they all arrived.
Numbers Chapter 13
For the past few decades it has been highly recommended that potential olim, immigrants to Israel come a few months or year before their actual immigration date to check out locations, schools etc. Nefesh B'Nefesh and AACI along with other immigrant organizations assist in planning these visits to facilitate an easier more successful aliyah.
They weren't sent out to discuss the pros and cons of living in the Holy Land. They just needed to prepare realistically. And they were supposed to bring back souvenirs, like the grapes, to show their tribes how wonderful the Land is.
But except for Calev and Yehoshua they failed miserably. They sinned and in that they were punished by Gd, and only the next generation was allowed to enter the Land.