Every time I say "by and large", I remember that the expression, which is generally understood to mean "generally" -- see what I did there -- is of nautical origin. The UK's Royal Navy created many figures of speech we use today in entirely different contexts.

"By" means "sailing close to against the wind", and "large" means "sailing with the wind behind us".

A ship that sailed well "by and large", was a ship that could do okay regardless of which way the wind was blowing.

i.e.: "Generally".