You might be surprised to know that sim owners, much like website owners and bloggers, do not automatically get paid for what they do. In fact, they pay for the space they use to give you the experience they give you. If there’s no advertising or product to sell, they rely on tips and donations to pay for running the sim (or website). A sim costs 2000 Lindens a day to operate. Therefore, a 50 Linden tip on a popular sim is quite a good way to help toward their goal to break even. Of course, the more you can spare the better.
If there’s a clear product or service the sim owner is selling, then, of course, tipping isn’t required. You know that when it is free for you to enjoy the sim, the cost goes out of the pocket of the owner.
Another thing you can do to help the owner is to spread the word on your favorite locations, tell your friends, maybe even blog about them. This is important especially when the sim is new.