Exactly what you need as a GM. All the reference material, charts and tables right at hand to make things easy.

I currently run a Deadlands: Noir game on roll20

These inserts are a god-sent for that game as they provide a quick reference to material I am other wise unsure of (such as patter and interrogation rules).

While they are over priced (the rules are in the book) I found them useful in keeping pace with my players.