Dropbox is free, though limited storage on the free plan. OP isn't necessarily recommending Dropbox in place of Google, but they're using Dropbox only for documents and such, which don't generally take up a lot of space. Their usage of Dropbox means they don't have to worry as much about losing important documents this way. I don't think it's an ad.

I totally agree, though, that it's just not a very useful tip. There's too much potential to cause problems larger than the one you solve.