One of the more interesting aspects of this hobby is the economic side of things. Reef keeping has a substantially higher turnover rate than most other hobbies, so it's not uncommon to see someone that's financially comfortable jump all-in over the course of a few weeks buying top quality everything, only to get fed up with the difficulty and quit the hobby 2 months later, selling everything for significantly less than they paid. At any given time, you can find the latest version of just about anything very lightly used for 35+% off retail on the forum classifieds and CL. This is especially true with the "leaving the hobby" type posts where people are trying to move everything in a hurry. Granted, in some cases, items are beat-up and abused, so it's all about keeping your eyes open and look for something in good shape for a good price.
Personally, I always look to pickup whatever I need second hand and will often snag things up if the price is right, even if I don't have a use for it at the time. There are some things I won't buy used like heaters, supplements, food, or just items that aren't very expensive to begin with though. I have no interest in saving $12 on a used heater or buying some dude's half empty bottle of Reef Roids.