When you use --user option with pip, the package gets installed in user's folder instead of global folder and you won't need to run pip command with admin privileges.
The location of user's packages folder can be found using:
python -m site --user-site
This will print something like:
C:\Users\%USERNAME%\AppData\Roaming\Python\Python35\site-packages
When you don't use --user option with pip, the package gets installed in global folder given by:
python -c "import site; print(site.getsitepackages())"
This will print something like:
['C:\\Program Files\\Anaconda3', 'C:\\Program Files\\Anaconda3\\lib\\site-packages'
Note: Above printed values are for On Windows 10 with Anaconda 4.x installed with defaults.