What are the differences between GSVA and ssGSEA (in layman's term)?

Question

[cwwong13]

I know the Bioconductor vignettes for GSVA has a decent description of the methodological differences between the algorithms. However, I am still confused with the technical terms. May I know if there are any further references that explain these algorithms in layman's terms?

1. I am interested to know if there are certain scenarios in that either algorithm has been proven (or suggested) to perform better.
2. Whether the "scores" derived from these algorithms can be interpreted in a similar way? I found that GSVA scores tend to center around 0. May I know if this is an "artifact" (or intended output) due to its algorithm?