CPT during undergrad allowed me to do summer research. OPT after undergrad helped me stay near campus and get paid for research while finishing my thesis when I couldn't afford the last semester of college. OPT after grad school is what kept me here for my first 3 years as a postdoc.
The US President's new proposal to tax international students has been approved by the White House for release this week. It's an unprecedented $100,000 tax on int'l grads who stay to work after graduation on Optional Practical Training (most grads do), a crucial bridge to remaining by any channel.