It depends a bit with which main app you work, or if you work only with Studio. Generally speaking in Maxwell they are called MXS references. So you have a Maxwell scene file, which can contain only one object, or 10, or however many you like, and you can import that as a reference into your main scene. The exact way you do this depends on your main app. Have a look in the plugin docs for details:
The other way you work in your case is to simply use instancing. You have just one copy of your real chair and table, and then you instance them in your scene. This way the RAM used when rendering is as if you only had one real copy of that geometry in the scene, even though you may have 10 million instances of it rendering. Basically the two main differences of working with MXS References vs Instances are:
– an instance can only instance a single object, not a group or several objects.
– for instances to work, you need to have at least 1 copy of the real object in the same scene.
So in many cases MXS Refs can be more practical. For example in your case, you might arrange 1 table and 3 chairs in the same way in an MXS scene. Then you reference this scene into your main scene, and you only need to copy this reference (or you can actually also instance an MXS reference) 40 times.
If you were using instances you would have to first instance and place 40 tables, then instance and place 120 chairs.