By and large means mostly, in general. By and large it works, by and large they agreed, by and large a success.
It is nautical in origin and precise in its old sense: by meant close to the wind and large meant with the wind behind, so a ship that sailed well by and large handled well in both. The modern sense is simply on the whole.
1phraseby and largeMostly; in general.
“By and large, the students enjoyed the course, though a few found it too hard.”
by and large is a qualifier.
From sailing, where by meant close to the wind and large meant with the wind behind.
From sailing: a ship may (or may not) sail well both close by the wind, and large, downwind, with sheets extended.
Etymology from Wiktionary, CC BY-SA
Practised in Small Talk & Everyday Phrases