In the latest Xcode @synthesize is optional. By default, omitting @synthesize is the same as writing
@synthesize someName = _someName;
The only reason to use @synthesize is to rename the instance variable created to store the value of the property, for example
@synthesize someName = someSpecialName;
When you use self.variableName to access a variable, you go through a property, which is a short method that accesses the instance variable for you. Although the method dispatch is very fast, it may perform additional services for you, such as synchronizing the access to the variable (this is the case when you specify atomic or do not specify nonatomic in the property declaration). In cases like that, the access through self.variableName will be somewhat slower. If done in a tight loop, this could potentially make a difference. That is why you sometimes want to access the underlying instance variable directly by using _variableName.
