Dropbox and Box Metro Apps

I noticed in the SkyDrive metro app if u right click u have the option to browse and add files and folders eliminating the need to have the desktop SkyDrive app on ur PC.

I also use box and dropbox as well and im noticing there's no option to add files or folders within the metro apps. Am I overlooking this?

I have the desktop apps for both of those apps as well and im noticing the more files I add to them the more space they seem to take up on my hard drive. Is there a way I can add files to the dropbox without having them take up hard drive space? It seems like I have my computer hogged up wit duplicate files because of dropbox.