For example, I started using FreeAgent for taxes and the game changing feature for me is the (Open Banking based) transaction feeds where transactions are pulled daily from multiple bank accounts, where you're prompted that you need to explain/categorise each new transaction and the explanations + transactions get locked-in once they become part of a submitted tax return.
You can easily change the category of a transaction in the UI but e.g. deleting or modifying a transaction amount will require multiple steps and for you to ignore loud warnings. The automated import takes care of avoiding duplicates and making sure nothing is missed compared to doing it manually.
I've done accounting with just spreadsheets before and I hated how easy it would have been to make an accidental edit and not notice. Manually exporting and importing CSV files is fatiguing and error prone as well.
I find this similar for invoicing software: you could keep a spreadsheet of who you need to invoice, if you sent it, if it's been paid, sending late reminders etc. but there's a lot of freedom to make mistakes and mistakes here are high impact. Invoicing software automates many of the steps, forces you to follow a set process and gives loud warnings if you deviate or make unusual edits.