1. Find a machine that does not have the Android SDK set up
2. Run the set up of Android Studio from the website (use express settings, which installs SDK into Library folder) - https://developer.android.com/studio/index.html
3. Open Unity project and switch to Android platform
4. Go to Unity --> Preferences--> External Tools (or Edit --> Preferences if you are on Windows), note that SDK is empty, try to select it by browsing

Actual result: You will not be able to find the SDK folder without using workaround of some sorts (running "chflags nohidden ~/Library/" on macOS for example)
Expected result: If the Android SDK is in installed in default place, Unity could check for the file path and use it automatically. If the user has installed SDK to a non-default place, they would be able to see the folder and select it, this would make the user experience better

Reproducible with - 2018.1.0a5, 2017.3.0f1, 2017.2.0p4, 2017.1.2p3