As many private business's, and governments, have discovered, money circulating through your own system generates returns far above the nominal value of the cash concerned. On the other hand money spent on anything outside of your sphere is influence is lost.
Foreign aid given to an overseas country, with the condition that it's spent on goods and services from the donor country is mutually beneficial.
Any goverment department spending money should have, as part of it's remit, to ensure wherever possible, that some of that money should be coming back to it's home economy. Even if at first sight that's not the cheapest option.