text: if you buy items for a business, you can claim they are a "business expense" and deduct them from your gross income when you pay your taxes.  so, you only pay taxes on a smaller amount of income.  for personal expenses, you can write off the interest on your mortgage, and a bunch of other thigns that I don't know about since i am not an accountant... but even things like moving expenses can apparently be written off your annual gross income... so then you only pay taxes on a small portion of this.