Let me preface this by saying, I'm taking about the sole proprietor/small business level, not large corporations.
Something I hear all the time is "my accountant says I need to buy (whatever) to avoid paying taxes." Half the time the person saying this is basically financially illiterate and I just want to shake them. Far too often people end up spending 100% to save 30%. If you truly NEED the equipment, then by all means buy it and write it off, but often it becomes a trap of constantly purchasing new equipment to avoid paying taxes, while not looking at the bigger financial picture. Farmers and contractors unfortunately can be a classic example of this. Full disclosure, I'm a contractor and farmer myself, but I do also have a degree in economics and farm business management.
I've known a few that the following has happened to almost verbatim, the situation plays out like this: Farmer Bob has farmed all his life, maybe even inherited the land, finally worked up to making a pretty hefty gross income. Along the way the advice was to "not show a profit" so he's constantly been reinvesting in new equipment, new trucks, buildings, etc (things which are all going down in value BTW). Every year he has to just spend more, more, more to avoid the evil tax man. Instead of investing in retirement accounts, mutual funds or other investments (because who trusts the stock market) he's just building net worth through land and equipment. Then it comes time to retire. No real cash in the bank since it was all spent on 'things' and no retirement accounts for the same reasons. To add insult to injury, no social security because he showed the net income of a pauper despite grossing six figures. So what's left? Have an auction, sell off everything for pennies on the dollar, sell off all the land, and MAYBE have enough to buy a house in town and live a few years on. Like I said, I've seen this first hand, more than once.
I have different strategies for my two businesses and do buy new equipment from time to time. However, having a business that is completely solvent and not investing too much in things that go down in value is critical IMO. If I have to pay some in taxes to invest in non-deductible/non-tax deferred investments then so be it. Putting EVERYTHING back into the business and ignoring the big financial picture is a pitfall that is all too easy for the small businessman to make...