Text expansion saves time. It's really that simple. Rather than typing out a lengthy word over and over, like a regularly visited URL or an embarrassingly long middle name, save it as a text expansion so that pressing a few pre-determined characters will insert that word instead. Google's keyboard comes with this functionality available out of the box, as do some alternative third-party keyboards, but this requires commitment to one of these options.
I'm a huge fan of text expanders. Seriously, they are necessary to me. As a regular user of both Mac and Windows, I have sought out solutions on both platforms and rely on them daily. That's why I've always felt horrified that there weren't any great options on Android. After all, mobile devices are already input-impaired, it only makes sense that we need quality shortcuts. As it turns out, such a shortcut has been under our noses for quite some time, tucked away where few would look and only available with the stock Android 4.1 (or higher) keyboard.