When purchasing range hoods, water heaters and gas stoves, you must issue an invoice, because the invoice is one of our later warranty certificates, and it can also prove whether the range hood, water heater, and gas stove purchased are from regular channels. Incoming goods. Invoices are very important. Invoices are an original proof of recording business activities. Invoices are an important means to strengthen financial accounting management and protect the security of national property. Invoices are an important basis for tax audits. Invoices are an important tool for maintaining social order. When we buy anything, we must ask the merchant to issue an invoice to ensure that our rights and interests are not infringed, and to supervise the merchant not to evade taxes.