It depends on your personal preference. Using Lightweight desktop environment is good for you, if you bother in even small delays in application startup or when you open multiple tabs on browser and at the same time, Pleasing looking (often called eye-candy) desktop is not in your personal preference.
But, If you are asking about the usability issue, I would say similar also. For example, Unity has some handy shortcuts for your favorite applications saved in the launcher. And I personally like the scale feature of compiz with lower-right edge enabled. (Whenever you bring your cursor at that position, You will be shown all opened windows scaled). Also, compiz is there because, it provide eye-candy desktop effects as well as some very useful usability handy options.
Let's see some examples ( from default settings ):
You can't take a screenshot with keyboard shortcut in Lubuntu by default. (Of course you can configure your pc later), but in Unity if you want a screenshot of a whole desktop just press PrtSrc. There are shortcuts for taking screenshot of a window and a specific area too.
You can't scroll the pages of manual with mouse, because LXterminal does not support scrolling with mouse. I think, this is a good usability loss.
The text editor included in Lubuntu is leafpad, though it is very fast and lightweight, it is missing some very basic functionality also such as syntax highlighting, spell checking etc.
I personally wouldn't use Lubuntu on a very capable new computer. I'd say, taking the advantages of latest technology to improve your productivity and the computer's usability is better, if you have a capable machine. In my opinion, you are definitely missing some usability and productivity tools by opting Lubuntu. But in final, as I said, it is all up to you. If you are happy with it, It is good for anything