Hi Rafael, We developed energy optimization algorithms and tools and in my experience i've seen improvements (talkin about operative margins here) between 2% and 20% depending on the assets mix, the size of the application and the flexibility allowed to run everything (sometimes security contracts or other policies requires machines to be always ON reducing the flexiblity margin)
Some companies tend to run with a business as usual approach because they don't have the bandwidth to really analyze and apply models to improve efficiency. When they do they usually have higher returns as there are many aspects that you can look at to optimize the system.
Larger companies, with more resources working on different aspects, have already optimized some aspects leaving less room for improvement. Consider though that a 2% savings in fuel costs for a large utility managing a power plant it's probably worth more than a 10% improvements in smaller plants so it's kind always worth looking at solution to optimize the system.
I hope this gives you some perspective.