Take an extreme example - 3D Studio Max by Discreet Software.
3DS Max can be owned for the low, low price of 3,495 dollars. It costs way too much for the normal home consumer to buy. So if you are someone who just wants to "check it out" you can either warez it, or forget about it completely. Either way the company is getting no money from you. You can't point to that burnt copy of 3DS Max on your desk and say "you owe Discreet Software 3,495 dollars", because if you didn't warez it, you wouldn't have brought it anyway so Discreet didn't really miss out on a sale.
What you do with that copy, can be good or bad. If you make a copy of it for a person (or company) who could easily afford to buy the software, you are denying Discreet a potential sale, which harms their business. If you mass warez it and sell the software online for 100 dollars a copy, you are harming Discreet's business too. I also consider selling warez to be very immoral because you are making easy money from someone else's hard work. However, if you just keep the copy for your own personal use, it can end up being a good thing for Discreet. If the software really is good, really is worth buying (if you can afford it), then you will recommend it to other people and even your employer. These recommendations you would not be making if you didn't have that warez copy to check out in the first place.
Core2 Q9400 @ 3.0, eVGA GTX 260, 4G DDR 800, Vista64