The fret is the point that the string vibrates against to produce a note. If there is extra string between the fret and the point where your finger pushes down the string it is likely that the string between your finger and the fret can cause a “buzzy” or “muffled” sound. If you are having trouble getting your notes to ring “clearly” try this tip.
You will also find that you won’t need to press as hard to produce a note if your fingers are near the frets. This is because it takes quite a bit of energy to push down that extra string to the point where it won’t “buzz”.
There is only one exception to this. You may find that sometimes it is nearly impossible to keep several of your fingers near the frets when you are playing chords, especially when two fingers are required on the same fret. Just get them as close as you can and you should be OK.
Happy fretting! -Bob