Matthew Poole and continuators on Joshua 13:29

29 And Moses gave inheritance unto the half tribe of Manasseh : and this was the possession of the half tribe of the children of Manasseh by their families.

Not that they desired it, as Reuben and Gad did, Numb. 32. 1. but partly as a recompence to Machir the Manassite, for his valiant acts against Og; and partly for the better security and defence of the other two Tribes, by so considerable an accession to them, which also was without any inconvenience to them, because the Country was too large for the two Tribes of Reuben and Gad.