The purpose of the regulation was originally to secure tax payers, but during the early Heian period, onshu and kasshutsu were used as a legal loophole to migrate to the Kinai region (provinces surrounding Kyoto and Nara) where the tax burden was lighter than in other provinces.
本来は課役負担者の確保が趣旨であったが、平安時代に入ると陰首・括出は地方より税負担の軽い畿内に移住するための法の抜け穴として利用された。