With processors and graphics cards and general hardware improving rapidly, 3D modelers are packing in more and more information into their models. Detail to objects is being added into the geometry which wasn't possible a few years back. We take quite a lot of our 3D models straight out of Revit and we therefore regularly deal with models in excess of 15 million polygons! The past few years have helped me develop some techniques which enable me to handle these large scenes and even output them into interactive scenarios on tablets too.
When your scene polygon count is out of control and you're trying to cut it down, the first thing I do is find out the statistics of the scene. If you press the shortcut 7 on the keyboard you will notice in the top left-hand corner a set of yellow numbers. This tells you what's in your scene. It can then be customized by going to Customize Viewport and the Statistics tab. Then set it to Total + Selection. Finally, make sure that Show Statistics in Active View is selected.
Statistics will keep you informed about the state of your scene
If I have received a scene from an external supplier, and it's been built in something like Revit or SolidWorks then the first modifier I go to which is an absolute life-safer is the Pro Optimizer modifier. This is a quick and stable way of quickly cutting down the polygon counts of your models. It's as easy as applying the modifier, and adjusting the percentage value to your desired level of detail. You can also tell it to preserve vertices if you want.
This modifier is perfect for those objects which are far away from the camera and don't need so much detail
Use asset tracking
As scenes get larger, sometimes it's difficult to keep a track of all the XRef's and materials and external files that are referenced in. 3ds Max have given us an excellent tool called Asset Tracking which lists out all the references. What is also neat is that it allows you to change the locations that those files are referencing. The asset tracking can be opened using the Shift+T shortcut combination.
All of your assets are organized in one handy place. Use the asset tracking to make sure all your assets are correctly linked
Auto updates of material swatches
If your scene is large than the likelihood is that you'll also have a large array of materials. If those materials are particularly complex then you may find that your computer takes time to auto-update the material swatches. This can be a massive time waster. To get around this you can turn the auto-update off specific materials if you want. Simply right-click on the node and deselect Auto-update.
This is a simple adjustment which can help if you have lots of complex materials in your editor