Bust dart
A bust dart is used to match the side seam lengths when the front part has been reshaped due to a large bust measurement (or bust ease value).
By default, the bust dart is enabled but will only appear if the bust measurement is large enough.
When you disable the dart, you will have to match the side seam length to the side seam lengths some other way. For example, with gathering or pleats or by constructing your own dart.