Some time ago, forward=True was made the default for set_size_inches: #4680

However, this left set_figheight and set_figwidth with forward=False as the default. The original "it makes more sense" argument still applies here, but with the added (and perhaps more important) motivation of making all three methods consistent.

For example: A user changing the size will find their bounding box updated automatically, but when only changing the height or width, they will find the bounding box is not automatically updated. This is highly unintuitive.