The limitations impede the recipient country's ability to find the most cost-effective way to spend the aid they receive.
Furthermore, tied aid often favours capital-intensive goods and advising primarily in the donor country's area of expertise.
That may lead recipient countries to make purchases which are inappropriate for realising their development goals.
In addition, the administration of tied aid requires larger bureaucracies in both the donor and recipient countries.
Untying aid would presumably give recipient countries greater freedom to choose how they spend their resources, focusing on the goods and services they need most and allowing them to purchase from the most cost-effective sources.