I have seen pros and cons for cutting the strips to size - and I did a block the two different ways (1 block each) - I found that while the free cutting (let's call it) made me feel good and produced a nice block - - the pre-cutting the lengths helped me to stay "square" - - prevented me from getting just that smidgen off that you don't notice until it has exaggerated itself over a couple of rows. In spite of the fact I am a new enough quilter to get queasy about cutting too many blocks or strips ahead of time - - I found my best block in the experiment to keep me on track was to cut the strips to size in advance.
Anyway, I will probably still go ahead and do it as the mood hits me. :-)
Marysewfun