I dont really undertand how interval-padding from GenotypeGVCF works

Question

[ManuelDB]

I understand what the tool does when you add interval-padding 100.

What I don't understand is how this works considering that the file input in GenotypeGVCF is a gvcf file. I could imagine what this does working with bam files or another similar file that contains the reads but as far as I know, what do you expect to find if you expand 100 or 150 bp when you already have your variants called from the input file?

I don't see the point.