Can Online Study Tools Improve Understanding?

I've been thinking about how much learning has changed over the last few years, especially for children and adults who study independently. There are so many online calculators, converters and educational tools available now that it's easy to find an answer, but I'm not sure whether they actually help people understand the topic better.

For those of you who teach, tutor, or help children with homework, do you encourage the use of online learning tools, or do you prefer students to work everything out by hand first? I've found that simple calculators can be useful for checking answers and reducing mistakes, but only if they're used as a learning aid rather than a shortcut.

I'd be interested to hear what has worked best for others. Are there any educational websites or tools that you've found genuinely improve understanding rather than just providing quick answers?