subdomains pointing to main domain directory (one source code) VS source code for each subdomain

i'm currently using wildcard subdomains which pointed to main domain (i use only one source code in the main domain which can handle the subdomains). someone told me to copy source code in each subdomain to reduce access to the main domain because over time the site becomes slower, he said also Exp: one click of a button for 200 or 300 Internet users, the requests will enter an execution spool which causes slow response from the client. i don't know if this true or not ! and i have to choose only between those two solutions, can you tell me please and thanks.