Work in Series?

I’ve been working on a series of works for a couple of years now I loosely title them ‘Map Drawings’ as they are all drawings on maps. Working in series has brought up some questions though. This series has become a comfortable set of work, which I can easily go back too and fit into again, it’s become my comfort zone. This phrase ‘comfort zone’ has always felt negative and maybe it doesn’t have to be, maybe while restricting yourself and limiting your parameters great things can come from it too. I remember having a great quote that illustrated this but I can’t find it now so I’ve found a few more:
‘Each repetition has a new meaning’ --Gandhi
Limits increase creativity. --Kim Stimpson
‘Repetition is the mother of all skill. --Anthony Robbins

Or am I just in denial? All the great artists are put into boxes of what they are known for, we all do it go round galleries guessing who’s work that is and more often than not it’s easy to guess because of their style, their comfort zone of work is easily noticed.
Maybe because I keep coming back to this series it means it’s not finished, maybe it won’t be done until the last piece is completed. Does there have to be an end, it can be organic, just go with the flow and work to your own rhythm not dictated by anybody except yourself or at least your subconscious.
What do you think? Why do you work in series? Why don’t you work in series? Is it important?