When and when not to create SP/triggers

Hi, I am having trouble deciding when to (or when not to) create stored procedures and/or triggres. I know they are useful and there is overhead involved. We have PB application and all PB developers bug the hell out of me to create triggers and SPs. How do I decide if an SP or trigger should be created or not created. When I ask PB people why do you need it, I get "to reduce network traffic" response. How can I get a better grip on this issue (books are not helping me much!) ? Thanks. Keith