LESS is more?

Recently I've been exposed to LESS which is a UI framework.
In a nutshell, this framework extends the standard CSS in a way that insert programming flavor into it, such as inheritance, variables, functions and build.
(By the way - this is not the only framework with such concept)


Using this framework has some pros and cons which I would like to highlight.
Pros:

• Enable css reuse via inheritance, variables and more.
• Build *one* css for the final html to use.

Cons:

• Introduce another development language, which requires strong CSS knowledge (if you use it well, otherwise, no point to use it)
• End-to-end developers (UI to server) might need another domain to maser
• Coupling your project with another framework. Disconnecting from less is not simple
• Produced css are not ideal for development phase and debug
• CSS changes can be done only via this framework/language

At first review this LESS technique sounds like a css simplification magic, however at the end we stopped using it since its cost/benefit was low.

Please let me specify my claims.
The main disadvantage of this framework, IMHO, is that it makes your project too couples with it.
While the generated CSS is ideal for production, in development environment, it's very hard to work with.
In a typical project where several UI frameworks (e.g. jquery) are involved - imagine how long the one output css file will be.
Moreover, not only that it would be very hard to work on the CSS output directly, it would be very hard in the future to separate it to file per framework since LESS does not support it.

Another disadvantage is that in order to use this framework properly, the developer need to learn another language and expertise in a domain which is not necessary the developer strong side.

This tool is mainly used by UI side people, so knowing that tool is like Java developer to know Spring framework, however, this does not work the other way around - for Java developers such tool added complexity. It is one thing to know JS or modify slightly css, and another thing to have experience in CSS inheritance and advanced techniques.

I think it applies for LESS developers as well. How many UI developers do you know who master Spring or Hibernate...

Anyway I hope my experience would help other to estimate whether to use such framework or not.