Writing, by definition is a solitary occupation. All that time spent doing research, plotting and maybe even world building is usually done by the writer alone.
The countless hours crunching away at the keyboard as the word count slowly ticks along towards a big enough number or perhaps, as for me, when I have finished the story. Those two instances are not necessarily the same, I may blog on that at another time.
This is where, at some point, the writer needs support and third party interaction and not just from beta readers. A writer needs to “feel” that they are a part of something and not apart from others. Being a member of a writers group, or several writers groups takes on a significant role in the writing process as a whole.
People in writers groups have a wide and varied breadth of knowledge and more often than not are willing to share their expertise with fellow writers. A tip here, a prompt there or a different slant on your project can pay great dividends.
Above all, being in a writers group gives support and comfort to the lone writer and that above all is worth its weight in gold.