Using unsettled cash to buy securities on Interactive Brokers

From Interactive Broker’s Availability of proceeds in a ‘Cash’ type account article:

Account holders who wish to have access to settled funds prior to the settlement day may do so by electing an account type of ‘Margin’. Under this account type unsettled funds may be used for trading purposes but may not be withdrawn until settlement.

How would this work? Is it a loan on which I have to pay interest for two business days until the first trade is settled, or just because the account is of margin type, I am entitled to use the funds faster than the usual settlement time?