If you need to focus on a certain project/phase/client, you can easily limit your view to only a subset of your task hierarchy.

Right click on the desired parent in the Timeline view and select the "Limit view to this" menu.

Your list of tasks is now limited and a Badge is present on top of your list.

You can simply click the cross next to this badge to remove the limiting of the view.

The limit will be also kept in the List and Board views.