You don't need to BUT I feel like you must understand why you don't need to in order to make that creative decision.
I think most of the consensus is "you can go as simplistic as you want", it can work but you gotta know what you gain and lose from that decision.
And from what you are sacrificing, you have to find solutions to make those losses, a win.
I've read so many webtoon that made the "creative decision" not to be detailed with their art just because of efficiency (or lack of skills) and it affect their decision when it comes to tell their stories.
To give you an example, if you go for flat colors no lighting, no shading, would you be able to portray certains vibe and effect that can only be done with lighting and shading ? If not, can you utilize the pros of your creative decision to make your intention happened ?
In that scenario, are you confident with color theory to the point that you can play with it for specific emotions ?
Another example which is a bit off topics but it's about backgrounds, some artists decide not to spend time on environments because of lack of time. But then, are they aware that environment can be a great tool for storytelling ?
Almost everytime I read a comic that made this creative choices, end up having a bland way of portraying a back and forth conversation.
It's already hard as it is with backgrounds, I can't imagine without any xD
At the end of the day, to be "successful" you have to make people feel that your creative decisions were made out of confidence and that you know what you are doing.