When an attempt is made, for example, to mate two components to have parallel faces set coincident, SolidWorks may present the user with an "error" message such as: "Planar faces are not coincident. Separation distance is 0.0806163mm."
Unfortunately, although the message is factual, it is NOT complete and is potentially misleading, since the root cause is unidentified.
The reason the mate is not possible stems from the fixed conditions of the components within the assembly. By floating one of them, the mate can be applied without difficulty.
The enhancement, therefore, is for the mate function to provide more detail in its messages, so that the user can, for example, be reminded of the limitation(s) created by a pre-existing FIXED condition. Although the Feature Manager shows fixed status with (f) before the component's name, this is not always immediately obvious when the component (selected from the viewport) happens to be far down in the sub-assembly tree.
Note: This, for example, is really no different from the notice provided by the current messages which refer to a new mate as overdefining due to the existing (fixed by mates) relationships.
Perhaps the selected face (or other entity) of the fixed component could be flagged within the Mate Selections Dialog Box in a way to show the immovable condition. This would serve to remind the user of the need to restore floatation in order to achieve mate success.
If you agree with this sort of enhancement, please put in a request to SolidWorks.
Per O. Hoel