That structural difference produces all the practical ones. Bank feeds arriving automatically rather than being typed. Reconciliation against your actual statement, which is what catches missing and duplicated entries. Reports generated rather than constructed, so a profit statement and a balance sheet exist correctly rather than being assembled by somebody who might have extended a formula one row short. And an audit trail recording what changed and when.
A spreadsheet remains genuinely adequate in narrow circumstances: very few transactions a month, no employees, no inventory, no sales tax collected on behalf of anybody, and no intention of borrowing. Below that threshold, software is a subscription buying capability you do not use. What ends it is rarely volume and usually complexity, and the specific triggers are employees, inventory, collecting tax, or somebody outside the business needing to see your numbers.
The cost of staying too long is not the bookkeeping hours, which are comparable either way. It is that a spreadsheet cannot tell you it is wrong. A category typed slightly differently, a transaction entered twice, a formula that stopped one row short, all produce a total that looks plausible. Nobody discovers it until a reconstruction at tax time, and by then the error is spread across twelve months.
There is a middle position worth naming, because it is the correct arrangement rather than a compromise. Software for the ledger and spreadsheets for analysis. Spreadsheets are genuinely better for modelling, forecasting, and answering one off questions, and the right pattern is to pull clean data out of the accounting system and analyse it there, rather than using a spreadsheet as the system of record.
If you are currently on a spreadsheet and expect to move, structure it now for that migration. One row per transaction, one thing per column, consistent date formats, no merged cells, no colour carrying meaning that exists nowhere else. That discipline costs nothing today and turns the eventual move into an import rather than a retyping exercise that takes a week and introduces its own errors.