How do companies deal with limitations and constraints of Twitter Bootstrap after choosing to use it in a particular project?
Web designers are no longer free to design Web pages. They need only to chose from Bootstrap components and how to customise them. If we give web designers all the freedom, passing from design prototypes to real html/css pages, it will cost a lot of work to adapt Bootstrap components to the desired look that was designed.
You are not forced to use everything from the twitter bootstrap bundle. It is an option, not a rule. If you want your own elements, such as buttons, but like some bootstrap elements (the grid system is very popular), extract only the parts you want and design the rest yourself.
Naturally, if you want to use bootstrap for everything, the designer is then limited by the constraints the frameworks presents and must adapt his design to match the bootstrap visual side.
From what you've said, I've understood: "if we use this tool, we'll be forced to follow its design choices. If we do not use it, we'll need to spend much more time creating our own design choices".
Reading that way, it becomes simpler to understand, don't you think? Twitter Bootstrap is a nice tool that helps you to build nice looking websites. However, if your design goals are very different from what Bootstrap offers, you need to build something new (that will cost more) or try another CSS Framework like Foundation or Semantic UI.
Web designers are no longer free to design Web pages. They need only to chose from Bootstrap components and how to customise them.
Also, you are diminishing the web designer value. Customising components is also an important and hard part. They need to think on UX and how to place components correctly. That's a hard and important role.
