It's just about efficiency.
Remember it is the fund, not the asset manager, that is the relevant legal entity from a regulatory perspective. A key challenge posed to asset managers by non-cleared OTC derivatives margin rules is managing segregation of collateral assets efficiently and securely at the fund level.
Unlike central clearing of standardised OTC derivatives under the European Market Infrastructure Regulation (EMIR), the new rules for non-cleared, non-standardised derivatives demand that initial margin should be exchanged on a gross basis. It should be held and made immediately available to the collecting party in event of counterparty default. The posting party is also protected should the collecting party enter bankruptcy.