Chandler Bing wasn't always intended to be a primary character on Friends. The core group of characters looked a lot different in the early stages of development for the NBC sitcom. If the writers stuck with their original plan, Chandler would have been largely absent, which would have undoubtedly hurt the balance of the long-running series.
It's very difficult to envision Friends without the equal presence of Ross, Rachel, Monica, Chandler, Joey, and Phoebe. Those six characters each received ample screentime as they faced the joys and challenges during their lives as twenty and thirty-somethings in New York City. Chandler served a key role among the group as his humor and sarcasm stood out from the rest. From the beginning, Chandler used his wise-cracks and quips as a defense mechanism. This behavior became synonymous with Chandler's character and it became necessary to balance the sitcom when interacting with his peers.
Chandler may have never been able to develop his sense of humor if the creators went with their original plan. Before the six characters made up the focus of Friends, Chandler and Phoebe (Matthew Perry and Lisa Kudrow, respectively) were intended to appear as supporting characters. The series was originally planning to put Ross, Rachel, Monica, and Joey at the center of the series while Chandler and Phoebe popped in time to time. This would have killed any chance as a long-term romance between Monica and Chandler. It would have been inconceivable for Monica to end up with Chandler had he not been a primary character.
The lack of Chandler's presence would have notably hurt Friends' humor. Chandler provided many of the laughs and his behavior frequently offset some of the more serious moments. There was no other character who could have filled that void when it came to playful banter. Using Chandler in a supporting role would have also affected the dynamic of Ross and Joey. Chandler stood as the mutual friend which brought the three of them together. He had a unique relationship with both Ross and Joey. The relationships throughout the ensemble of characters would have been altered if Chandler wasn't a mainstay.
Phoebe was frequently portrayed as an outsider so it's almost easier to imagine her character in a supporting role. She was eccentric and marched to the beat of her own drum, making her a reasonable candidate had she disappeared every so often. On the other hand, her personality was accepted and she became an important member of the main cast. Phoebe provided the show with her own wild sense of humor while her stories from her earlier life similarly resulted in sitcom's best gags. Just like the situation with the seventh friend, Pat the Cop, viewers should be thankful that the creators of Friends took the time to fully envision the characters who served as the foundation of the series.