Yea but sometimes details he deems unimportant might still be illustrative of the lives and times of people of that era.  War isn't all about fighting, and much of the more "boring" stuff is more representative of what they are really like. He might think people won't be interested in the time he fixed a faulty fuel line with fuel and fire hazards spilling all over the place, but it's still the stuff of social history.  Perhaps he won't tell you about some of the tristes going on at the time though - men are funny like that - what happens in war stays with the war mates even after they're dead...

Index of Frank's Diaries