Stuart Noble wrote

Here's the thing. Pro door hangers use a plane because often they
don't have the space to lay the door out on sawhorses or whatever
and, because they do sod all else all day, they're pretty good at it.
For the rest of us, and I include chippies who don't hang doors all
day long, the circ saw method is pretty foolproof

Like hell it is. The problem with using a circular saw is that it is
MUCH harder for someone who has never done a door before
to work out how much to take off. MUCH safer to trim the door
gradually with a plane until it clears the new carpet or tiles.