The first version of MacWrite was actually pretty limited, and could only handle a few pages of text before running into performance problems - however, it raised the bar on what users could expect from a word processing program. It spawned many imitators, including WriteNow, which fixed the limitations while adhering to much the same user interface, and it was the inspiration for the first Microsoft Word program, which originally only ran on the Mac - the DOS PCs of the time could not support the high resolution display required for WYSIWYG. MacWrite also established the conventions for a GUI based word processor, with a toolbar for selecting paragraph formatting options, font and style menus, and a ruler for tabs, indents, etc.
The original Mac could print to a dot matrix printer called the ImageWriter, but quality was only adequate rather than startling. The later LaserWriter laser printer allowed dramatically better output, at a price. However, the possibilities of the GUI/MacWrite/LaserWriter combination were obvious, and this in turn spurred the development of desktop publishing, which sealed the future for the Mac and GUI.
Apple were slow to develop MacWrite, and by the time is was rewritten as MacWrite II, and later MacWrite Pro (under the Claris company name by then), it had lost out to Word and others. MacWrite Pro continues as part of the ClarisWorks (later AppleWorks) office suite, which is still available for Mac OS X.