Cmd+click to grab a whole group
Hold Cmd (Mac) or Ctrl (Windows) and click. Maket works out what the item belongs to and selects the whole thing.
Click a piece of furniture → selects every piece of furniture in that room.
Click a wall → selects the entire straight run of wall it belongs to.
This is the fastest way to re-finish all the cabinetry in a kitchen, clear a room, or set the thickness of a long wall without clicking each segment.
Shift+click to choose exactly what you want
Cmd+click takes the whole group. When you don't want the whole group, use Shift+click instead: click the first item, then Shift+click each one after it.
Use it when you want four particular chairs rather than everything in the room, or two walls out of a longer run.