How bad does the government want to "get you" on drug charges?

I am aware that the summary of this question is convoluted, but it’s a question I often have. Federally, and in most states, marijuana is illegal. But if Seth Rogen goes on tv and talks about all the weed he’s going to smoke later on, nobody will give a shit and chances are the LAPD won’t show up at his door. If he tells a cop he’s going to smoke weed, the cop might search him. What about sending it through the mail? If I send my friend a bag of badly concealed herb—and it’s discovered in a routine postal service inspection—what are the chances the cops are going to show up at HIS door? How bad do they went to get us?