Don't think "sanding" think "scuffing."

Go over the varnish lightly to just scuff/scratch the surface with 220.

I use water and wet/dry paper so I can clean residue off with water instead of creating dust when I'm going to varnish next.

Scuffing does three things.

1- It tells you if the varnish has cured. If not it will clog your sandpaper.

2- It provides a mechanical "tooth" for the next coat to bond. This is what the manufacturers suggest. Don't be lazy!

3 - It gives you a clear view of coverage and spots missed.

I don't want to have a customer call me with a problem, so I do it this way.

In a hurry? Skipping steps is the best way to create more work trying to repair a problem, instead of taking the time to do it right in the first place.

If you know what you did right, it's also easier to figure out what's going on when something goes wrong.