One of the parts of the swing I like to see is when a golfer has a right foot that is flat at impact or close to it. Granted, with longer clubs this is less necessary and more difficult to accomplish, but if you can get somewhat close then that's pretty good.
As Homer Kelley states in 7-17 of his book 'The Golfing Machine', the foot action accomodates the knee action and that the heels should not be lifted off the ground, but rather pulled off of the ground by the momentum of the golfer's swing.
Essentially, I believer Homer wanted golfers to avoid getting their weight up on their toes because that meant the golfer was lifting their heel up off the ground instead of having the heel pulled off the ground by the momentum of the swing.
If anything, I think that 'lifting' hurts the pivot, can move the location of the low point, makes balance difficult and can overdo the tilting of the axis (spine) away from the target.
I always like to tell people who ask me about footwork to take their address position without a club, then get up on their toes with both feet. Now, try and pivot back and pivot thru. When you do this you'll find it difficult to pivot, but also difficult to balance yourself and you can only balance yourself when you slow down the pivot, which is not what we want.
I was reading over an old thread at John Erickson's Advanced Ball Striking forum and he said that the left knee and the right foot work in conjunction with each other. Meaning that if the left knee is flexed at impact, the right heel can stay down more at impact.
I wanted to check this out, so I looked at golfers who had a flat right foot at impact.
Here's a great pic of Hogan and Knudson at impact with a flat right foot.
If you look at impact, both men have quite a bit of left knee flex at impact. Knudson's foot is flatter than Hogan's at impact, but he also has noticeably more left knee flex as well.
Here's a pic of Grant Waite with a flat right foot at impact.
Again, flat right foot...bent left knee.
And then there's Moe Norman, probably the most exagerrated sample of a flat right foot at (and thru) impact.
But, I don't think we can just look at a few swings and pronounce this as true. So, let's take a look at the heel up off the ground players. And usually when I think of heels up off the ground at impact, I think of the LPGA Tour.
So, if you want to flatten the right foot at impact, take a look at your left knee. You may even feel like your left ankle is 'cocked' at impact. And that may help your right foot stay flatter and help your ballstriking.