With that base structure, you can start answering any questions by just summing entries groupped by accounts filtered by a regexp on fullname and fitler on date. What is my cashflow for any time period, what is my equity, what is my balance sheet, what I actually have, what changed recently, how any of this develops over time...
I wanted more pleasant entry. It became tedious/error prone to search for similar entries with vim and copy pasting. I could have made a specialized tool with nice autocomplete on top of ledger, but then why not drop the entire thing and use a database, where you don't need to re-invent groupping, sorting, filtering, summing, date interval operations and all the mundane stuff.
I also wanted to import data from a bank, and keep all the info associated with the entries. Easy to do in a database, not so in ledger text format.