The block of code itself is disconnected from the control statement which allows developers to comment out or remove entirely a control statement without having a large risk of encountering syntax errors because of extra or missing braces.
Since each bracket is its own line, the Allman style takes more vertical space than other indent styles. This is one of the reasons that a lot of book authors do not prefer to use Allman style in their texts.
Since the Kernel style uses 8 characters for indentation, the lines of code are pushed too much to the right. This may make it harder to read for small monitors (for example terminal monitors which are 80 characters wide).
With this style, one of the advantages is that the opening brace does not take a whole line for itself, wasting a lot of space. The closing brace though is indented on the same level as the control statement it belongs to, making it easier to understand which block of code it's closing.
The K&R style uses braces only when necessary. So for example: if(condition) doSomething(); But this can be annoying if you need to put something inside that if statement, because you have to go and add braces to make sure that will be grouped correctly with the statement that was befor...