I failed to understand why auto implemented property language feature exist in C# 3.0.
What the difference it is making when you say
public string Fi
The difference is that other assemblies compiled with code that read the property is compiled against a property.
If you later on decide you need to add code to the getter or setter, you can do that, without having to force every other assembly linked to it to recompile.
Not so with fields. If you later on change a field to be a property, in order to add that code, other assemblies linked against yours will cease to function properly since they're compiled to read a field, not a property.
Also, lots of code is written to find properties, not fields, like data binding and similar.