On Mac OSX Yosemite why does my computer download 500MB every day whether I am using it or not?
nsurlsessiond deals with iCloud &amp; also Spotlight.


for Spotlight - Prefs > Spotlight > Search Results &amp; switch off Spotlight Suggestions &amp; Bing Web Searches.
iCloud, some suggestions…


Disable iCloud Photo Library, Photo Stream &amp; iCloud Photo Sharing from
System prefs > iCloud - Photos [or equivalent, I can't remember the precise layout before Photos app]
If you have an iPhone, the same settings are in Settings > iCloud > Photos