Unlike models from HP which had been introduced a few months earlier and used their proprietary PCL printing language, the LaserWriter included the PostScript page description language which allowed for far more complex graphics, high-resolution bitmap graphics, outline fonts, and generally much better looking output.
The use of PostScript comes at a cost. Unlike PCL and other early printer control languages, PostScript is a complete programming language and requires a complete computer to run it. In the case of the LaserWriter this was a Motorola 68000 CPU running at 12MHz, making it the fastest machine in Apple's lineup, and the most expensive at $6,995.
At this sort of price point the printer needed to be shared among several computers. However LANs were both complex and expensive at the time, so in typical Apple fashion they wrote software to drive the Mac's RS-422 port at about 250kbps, wrote a protocol stack called AppleTalk to run on top of it, and delivered the result as LocalTalk (referring to the hardware, cabling and software).
When shared between several machines, the LaserWriter quickly fell to an attractive price point. It was unmatched in terms of printing ability, and could only be fully utilized under a GUI based computer, on which Apple had the monopoly at the time. Millions were eventually sold, and the LaserWriter is also credited with saving both the Macintosh, and Apple.