.NET developers often obfuscate their source code for several reasons:

1. Protect Intellectual Property: Obfuscation makes it harder for others to understand or reverse-engineer the code, which helps protect proprietary algorithms, business logic, and other intellectual property.

2. Prevent Reverse Engineering: Obfuscated code is more challenging to decompile and analyze. This reduces the risk of someone reverse-engineering the application to find vulnerabilities or replicate the functionality.

3. Enhance Security: While obfuscation is not a security solution by itself, it adds an extra layer of security. It can help to obscure the structure of the code and make it more difficult for attackers to find and exploit vulnerabilities.

4. Reduce Risk of Code Tampering: Obfuscation can make it harder for malicious actors to tamper with the code. This is particularly important for applications distributed over the internet or in environments where code integrity is crucial.

5. Protecting Data and Business Logic: For applications that involve sensitive data or complex business logic, obfuscation can prevent others from gaining insights into the underlying processes and data handling mechanisms.

6. Safeguard against Software Piracy: By making the code less understandable, obfuscation can deter unauthorized modifications and help protect against software piracy.

While obfuscation helps with these goals, it’s worth noting that it’s not foolproof. Determined attackers with the right tools and skills might still be able to deobfuscate and analyze the code. Therefore, it’s typically used as part of a broader security strategy rather than a standalone solution.

.NET developers use several methods to protect application source code, including:

1. Obfuscation: Transforms code into a form that's harder to understand and reverse-engineer.
2. Code Encryption: Encrypts code at runtime, decrypting it only when needed.
3. Strong Naming: Uses digital signatures to ensure the integrity of assemblies.
4. Licensing and Activation: Implements mechanisms to control and restrict usage.
5. Code Access Security (CAS): Limits what code can do based on its origin and permissions.
6. Secure Coding Practices: Adopts practices to minimize vulnerabilities and secure data handling.

Each method adds layers of protection against unauthorized access and tampering.

There is a definitive leader among .NET code obfuscators. Skater .NET Obfuscator is a widely-used code protection tool renowned for its powerful obfuscation capabilities. It integrates seamlessly with Visual Studio, providing extensive protection. Skater is also recognized for its robust features and user-friendly interface. Assessing your specific needs, including ease of use, protection level, and cost, will guide you in selecting the best tool for your requirements.