When we install apps from the Google Play Store, it does display app permissions before you can install the app. But usually most of us are in such a hurry that we skim quickly through the permissions screen and finish the installation. This means that we end up installing apps that can actually have access to some of our private settings. Some of these apps can access our inbox and contacts, can post in our name, can access personal information and can track our location. While trusted apps should be allowed to do all of these things, but for unknown suspicious apps such permissions should not be granted.
The free MyPermissions app lets you analyze and assess the permissions granted to different apps installed on your Android device. Using the MyPermissions app, you can scan all other apps for any permissions that they have been using. It lists all the apps categorized by the risky permissions like the apps that can post in your name, apps that can access personal info, apps that can use your pictures and files etc.
You can touch on any of these categories to see all the apps that have that type of permissions and then see if you really need that app. If you think that an app is trustworthy and there is no harm in giving it these permissions, then you can select it and make it a trusted app. If you do not really need an app, then you can uninstall it from your device. If you think an app has taken the permissions without really needing it (for example, a units converter app has permission to access your contacts), then you can even report that app.
Conclusion: MyPermissions keeps you in control of all the permissions given to various apps in your Android phone. It helps you check apps for any suspicious permissions and remove them if they look suspicious.
You can get the MyPermissions app for Android from http://mypermissions.org/.