People aren't using Adblock to conserve resources. They're using it to block ads and most are willing to take a performance hit to do so.
That's not why I started using Adblock. I started because the web became unusable on an older machine (5 years). The content wasn't any more sophisticated but it soaked up all the resources (CPU, RAM etc.) available. Imagine if you had a PDF reader that ran at 100% CPU and swapped all the time!
No one expected the cure to be worse than the disease. I couldn't believe it somewhat recently when I had to use an older laptop to find that simply running Chrome was completely untenable if ABP was installed.