I've heard that it isn't a good idea to do finish planing after sanding, as the sandpaper will leave a bit of grit in the boards that tears up your fine plane blade.
Worse, the grit can not only affect the blade it can mar the sole of the plane. This would be more a problem with wood body planes. Anyone who dulls a blade should be able to sharpen a blade. It is the first rule of edged tools.
Most of the time there isn't that much grit left to do a lot of damage.
The point is if you are using planes properly sandpaper tends to not be used. Even 600 grit and higher will tend to dull a well planed surface. If a plane can not get a spot smooth then a scraper may be the tool of choice.
jtk
"A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
- Sir Winston Churchill (1874-1965)