When developing the Ionic project, there is no need for neither the Android or iOS SDK, since you will get the same results from launching the project through the Chrome browser and setting the viewport settings to mobile with touch.
However, when the time comes to deploying the application to Android and iOS it will be required to install the native SDKs.
As mentioned in the Swift section, deploying to an iOS device requires Xcode, since it is the only way to get the iOS SDK. Unlike other non-native technologies (e.g. NativeScript), Ionic does not provide a way of deploying the app onto an iOS. This means that Xcode is the only option.
On the other hand, it is easy and simple to deploy the application to an Android phone, through the use of Android Studio to obtain the Android SDK.