Do you really need a p-trap on bathroom sinks?
The “P” trap (named after its shape, has nothing to do with urine) is there to prevent sewer gases from entering your home.  It stays filled with water to form a barier.

You need it.  Sewer gases are not good for you.  In the right concentration they can even be explosive.  Plus they smell really, really bad.

Everything that connects to the sewer needs such a barrier.  Some things like toilets have the barrier built in.  Sinks do not, so they need it in the pipe.

Your friend will eventually get a clog further down the pipe.  This time he won't have a convenient and easy to take apart P trap for whatever crap he washes down the sink to get lodged in, so he will end up having to spend a lot more effort to remove the clog.  Cleaning out the P trap (or just replacing it, if it was too gross to be worth saving a couple bucks) would have solved the clog problem just fine.