Since I haven't used a VTT please don't hurt rocks at my questions but...
Are they worth it over simply using Discord and a dice roller if you're more into theater of the mind (i.e. no figurines, hex grids, etc)? For example some folks mentioned keeping track of character sheets in D&D Beyond anyway.
Also what can they do for encounter generation and combat tracking? I've used Kobold Fight Club before which was neat, since I could create adjusted difficulty enemies on the fly ("create a medium difficulty fight for this group") and kept track of initiatives/AC/HP for the NPCs.
Also also - modules. For instance what does buying D&D bundles (not adventures but actual system books) actually unlock?