what is com.sec.android.providers.downloads? I happened to notice this app(?) had access to virtually everything on my Galaxy S3.
Seemed a little strange so I googled it trying to find out exactly what it was for.
I never did find what I was looking for but I did find several pages of complaints about its effect on battery life.
I would guess it has to do with the download-manager but that's just a WAG.

Can someone tell me what it's for?

Roy
all providers.downloads does is act as one of many content provider aps included in the android stock system to act as a security feature so that apps cant directly access other apps but have to use content provider apps to exchange data between eachother. 
 we all know apps by default cant access other applictions data. 
      Thats where Content Providers come in to play, acting as a buffer between your internal apps and data and all the other 3rd party apps which have potential to be rouge/malicious. 
      Without this bouncer there would be no telling how many insecure transactions would occur between our devices and attackers in the free world global enviroment we exist in today.

The app EZ Disabler pro version states this discription about 

com.sec.android.
providers.security

"this package is a core sytem service that handles secure reads/writes to/from the database in your device. It keeps rouge apps for accessing data in your device."

The android developers site has this info posted about content providers and their functions.

android.provider

Provides convenience classes to access the content providers supplied by Android.

Android ships with a number of content providers that store common data such as contact informations, calendar information, and media files. These classes provide simplified methods of adding or retrieving data from these content providers.

For information about how to use a content provider, see the Content Providers developer guide. link to guide below..
https://developer.android.com/guide/topics/providers/content-providers.html

By the way..ehem..
     infosec is the bomb!
         Check it out my geeks!

a technique for exploiting applictions involving decompiling apk files and checking out the contents of its AndroidManifest.xml file for any registered content providers as well as the smali files for all uris used in the app.

http://resources.infosecinstitute.com/android-hacking-security-part-2-content-provider-leakage/
        and below is a link to the sample apk they made for the training example on infosecs site.