Artists often work in series. This means the artist creates pieces that are related in some way. It could be the theme, the size, the materials, specific colors, or specific techniques.
When an artist creates a work the process oftens (dare I say usually) brings up many what if issues — what if I used a different color, what if I used this stitch instead of that stitch, what if I turned it on its side, what if I made it larger or smaller or a different shape. The what if question is what keeps artists moving forward, tweaking, changing, growing, learning. For most of us, the what if question is a compulsion. A driving force that leads us from one work to the next.
There is often no way to put all the answers to what if into one work. It would be overwhelmingly busy, fussy, disjointed, crowded. The logical result is create another work to explore what if. This results in a series of works.
Working in a series isn't always something that is planned ahead of time unless the artist knows the issue she is exploring is too expansive to be covered in one piece. Sometimes the knowledge that a series is the direction to go happens over the course of time, as the artist addresses these different what if issues. Sometimes it hits rather like a bolt of lightning that this work needs further exploring. And sometimes it is planned.
So sometimes it is easier to work in series because there is no other way to explore an issue fully. In my opinion, though, working in series should never be forced. It would seem contrived, overworked, stilted, forced. So working in series because the artist thinks she should work in series would probably be harder than just creating a piece and then moving on.