It is recommended that you should use only those applications which consume less system resources and fulfills your needs at the same time. One of the good things about open source is that you can always find an alternative, Thunar is a light-weight file manager that provides you with all features of a good file manager. As you know that default file manager for Ubuntu, Nautilus, is a very famous application and has a rich set of features. One downside is that it consumes lots of system resources and becomes resource hungry application in many situations. Thunar is similar to Nautilus but uses less resources as compared to Nautilus, and in fact, this is idea on which Thunar was born.
Run the following command in the terminal to install it.
sudo apt-get install thunar
Once the installation is complete, you can launch it from Applications -> System Tools -> Thunar File Manager.
Its offers a wide range of plugins which can be used to extend the overall functionality. Thunar is fast and responsive with a good start up time and directory load time.
It lets you perform all file management operations by keep lots of system resources free. Enjoy!