Could anyone explain the benefit of using Dc.js vs google charts API or d3.js? Crossfilter seems really cool - but since it's another library, what is it that Dc is offering?
Then, bugs surfaced after google altered login procedures. What should have been a simple JSONP call was replaced with a broken login page being returned instead of JSONP, that is: only if you hadn't logged into your google account for awhile. People who've never logged in or were logged into a google service were fine. Then they started throttling connections - per computer, per account, random without announcing it, etc. Debugging these things was frustrating.
So, in other words, a convenient feature becomes a liability very quickly.
dc.js marries crossfilter.js with d3.js -- that's it in a nutshell.
crossfilter allows you to group and filter your data in-memory very quickly, and potentially for a LOT of data See http://bl.ocks.org/milroc/7032589 for a good intro to crossfilter (launch the demo on slide #39 -- loads 36M flight records).
you likely already know what d3 does. dc.js makes it easy to generate dashboards where the user can interact with the charts (e.g. filter by Q1, Q2...see the NASDAQ example at https://dc-js.github.io/dc.js/)
If you don't need interactive charts that you can drill-down into, don't use it. If you do, this is the best of breed right now for this kind of thing. dc.js doesn't abstract away the d3 api -- you can still use it to your hearts content, but it sure makes these kinds of examples really easy to spin up with minimal code.
Your second paragraph appears to be the answer to their question, however. dc.js looks like it provides higher level constructs, so you're joining data to a bar chart, not data to a series of rectangles that you need to then make into a bar chart. That's great for people that don't have the time or inclination to learn d3, and since it sounds like you can still get access to the full d3 API, it sounds like it could be useful to people that do know d3, as it would give them good starting points for a bunch of types of graphs that they could then tweak at will.
Of note Dc generates d3 charts...so you can manipulate them to your hearts content. In my case, part of the tabbing functionality (context switch) is to destroy any in memory crossfilters AND hunt through the DOM for any d3 svg elements and delete them to aid browser performance.
(since the GP asked for both google charts and d3.js, the firewall answer was irrelevant)