Tracking categories let you tag transactions along a dimension of your choosing — property, site, department, vehicle — and then report profitability by it. Xero gives you two, which sounds restrictive and is usually plenty. For a landlord they are the answer to per-property reporting; for a builder, per-site job costing; for an agency, per-client. This is worth deciding at setup rather than later, because tracking applied from January tells you nothing about the previous year and retrofitting it across posted transactions is tedious. The common mistake is over-designing: people build elaborate structures they abandon within a quarter. Pick the one dimension you would genuinely make a decision on and use it consistently. Two well-kept categories beat six that are half-populated.