Originally when LED landscape lights came they were really expensive. Soon after retro fit LED bulbs became available but they were not good enough for professionals to consider using them. It took at least a few years for the retrofit technology to improve to the point where it could provide results on par with incandescent lights. Today landscapers use mostly traditional lighting fixtures with a retrofit LED bulb. For only an extra $20 – $30 versus the price of a regular incandescent MR-16 bulb you can create an LED fixture.
LED systems allow you to use as little as a 150 watt transformer where you needed a 600 – 1200 watt unit before. This allows you to recover some of your LED investment. 12 Gauge wire in single runs can be used versus often having a looped run of much more expensive 10 gauge wire. The LED lights operate on a wider range of voltages making them much easier to work with.