The Tips in detail

 "The more complex the model the more time it takes to handle."

Max usually does not save all information about the objects. Mainly it saves the information about the underlaying geometry and the applied modifiers - of course together with their values. This means on the other hand that complex modifiers will be recalculated every time you modify the object. This makes you train your patience and wanting more and more CPU-power. There are cases known to exist, where a very complex model could be designed and saved but not reloaded thereafter...

If you made your complex model to it's final stage, you can collapse it. This makes 3DSM to convert the entire model and it's modifier-stack into an "editable mesh" (there are more options, I'm aware about this). This has many pros and cons. The main con is that you can't revert this. Another thing is, that the scene-file might possibly GROW in size. This is due to the fact, that 3DSM saves all vertice-data instead of the modifiers.