Revenue is recognised when the company has delivered what it promised, which is not the same as when money arrives. A customer who pays up front creates deferred-revenue until the product ships; one who pays in 60 days creates accounts-receivable on the day of delivery.
Traders watch revenue because it is harder to manipulate than profit and because it tells you whether demand is growing. Profit can rise on cost cuts for a year or two; revenue growth is the part that has to come from customers.
Example: Northwind Tools ships $840M of tools in a year. Of that, $95M is still unpaid at year end and sits in receivables, and $30M of prepaid service plans sits in deferred revenue rather than in the $840M.
Related: gross-vs-net-revenue, revenue-recognition