Sforno on Genesis 46:31/ספורנו על בראשית מ״ו:ל״א

1אעלה ואגידה, that your vocation is the raising of sheep and goats. I will not ask Pharaoh to give you the land of Goshen. The reason I will not ask for this is to make sure that he will believe you when you say that you raise sheep. i.e. that basically, you are nomads. If I were to mention the land of Goshen he would think that you ask for this because it is good grazing land.