I'm trying to install the .NET Framework 4.7.1 in Visual Studio and I'm given the choice to install:
Do I need them both? What's the difference between each of them?
Here is the difference, according to
A targeting pack: lets your app target a specific version of the .NET Framework when developing in Visual Studio and some other development environments.
A developer pack: includes a specific version of the .NET Framework and its accompanying SDK along with its corresponding targeting pack.
In other words, for example: SDK 4.7.1 includes .NetFramework 4.7.1 and target pack 4.7.1. But if you want to target .Net Framework 4.6, you need to install the target pack 4.6
The .NET Framework SDK, is a software development kit (SDK) from Microsoft.
It is required to develop applications for the .NET Framework and it contains:
.NET Framework SDK is dedicated to developing applications for .NET Framework. When installing visual studio, this is enough.
Targeting pack is needed when You are targeting a particular .NET framework which is different from your currently installed .NET framework.
In the case of the targeting pack, let's say you build your application using .NET 4.7 but the client has .NET 4.5. For this type of scenario you can target the client's version even though you are using a higher version.
Here you can see how to target a particular .NET framework.