While working with large assemblies on Solidworks at some point of time there arises a need to scale down the entire assembly or scale up the entire assembly. Lets have a look on to how we can scale the entire assembly once it is ready. Ideally to start with it is advisable to do the calculations beforehand to estimate the assembly size.
Generally there are two types of design processes while working with large assemblies. The top down design approach and bottom up design approach. While working bottom up the engineer designs the parts first and then the assembly is created. So, it may happen that the assembly becomes oversize and hence needs to be scaled.

While there is a feature of scaling the design in Solidworks, it works only for parts. When the need to scale the assembly arrives we are left with two options.

Either to scale individual parts and remake the assembly or to save the entire assembly as a part file and to scale it. The later option can be used as a quick tool to check the assembly in its scaled state however ideally it is advised to scale each part. That way if there is a need for future design changes it can be done easily by accessing the part file, rolling back the feature, making the necessary changes and moving the rollback feature again.

However using the scale feature for a multi-body part file is a little tricky as it may disrupt the shapes of the bodies and hence the complete assembly.

In the scale feature there are only 2 inputs required from the user,
In the scale about option if the origin is selected it will scale the part about the origin and if there exists any user-defined coordinate system then that option can be selected if the user wants to scale the parts around that coordinate system.

The below image shows the reason the option of scaling the multi body part file about the centroid is to be avoided.

As shown, all bodies scale about their respective centroids and the assembly is disrupted. As in a multi body part file created from an assembly the mates no longer work just the parts are turned into bodies and assembly is turned into part file.

Then there is a check to be made if the user needs to scale the parts uniformly and the scaling factor can be entered (e.g. if the size needs to be uniformly doubled the scaling factor will be 2).

In rare cases when non uniform scaling is required, there are options to specify the scaling factor for each axis. As I have shown in the above image the same multi body part scaled in y axis with a scaling factor of 0.5.