Browser-only software is easy to start with and stops when the connection does. A desktop app can keep working.
The counter
Symtex's Windows app holds an encrypted local copy of prices, customers and recent invoices, so selling continues offline and syncs later.
The back office
Reports, accounting and purchasing run fine in a browser, where a connection is normally available. Symtex opens in both.
Hardware
A desktop app is the natural home for barcode scanners, receipt and label printers and a cash drawer.