Decentralized Adapter Engine or Local Adapter Engine

Hi Experts,

I hv a doubt like what exactly we are achieving by installing a local Adapter engine? Is this something to handle the firewall protocols? In one of the SAP material, it has been mentioned that aditional adapter engines may need to be installed "Close" (in a network sense) to the Business System? What does it mean? What are the advantages over a centralized adapter engine?

regards