If I, say, create a round icon at 150px without any detail such as a drop shadow or glow, it will happily export at 150px.

However, this size is increased on export with the addition of a drop shadow or glow detail etc. For example, to 168px. (The same principle would effect a shape or text element.) Currently, using the same 150px icon with drop shadow example, the asset size on the artboard does not take this into account, but still shows as overall size as 150px, even though exporting increases this.

It would be useful to have an option to be able to design an asset at a given size to INCLUDE any detail effects.

This is particularly helpful for times when a specific size is required for a graphic asset, for example designing for an interface template with preset size allowances. Otherwise the user has to open up the graphic in Photoshop and downsize to fit (which loses clarity from the original).