In other words, type specification (T) is optional with default when the type can be inferred.
Depending on the context, the optional type specification can either clutter your code with redundant information or, on the contrary, improve the readability.
By default, ReSharper highlights type specifications as redundant and helps remove them:
If you prefer to have explicit type specifications in your code, you can change the corresponding preferences and ReSharper will help you add missing type specifications: