small meadows are fine for pastures. they end up costing way less.

The one problem I found with small meadows for pasture was that as the centre gets bigger it is more tedious to keep changing them out. Unless, of course, you invest in a farmhand to do it for you

For owning a large meadow that I have found out is that it's best for growing passes from your pass seeds. You don't need to add a trough or a tractor and the fertility doesn't matter either way...

.. but too also owning a large meadow is better if you have more horses than you have intended having for the achievement award in your trophy series.

You can only grow pass seeds on large meadows, and you should aim to have 6 large meadows with water throughs with the most expensive cows (Longhorn I think?), to grow leather. They will get you 1 million equus a month, even more if you make the leather into something like bridles or lunges

My suggestion is to get double the meadows you need. Say you have 100 boxes, you'd want 200 acres. Then put half into pasture and keep half off. Once those meadows fall below 100, lay them all fallow and then put >100 fertility in the filters. This would only show the meadows that have 100% fertility, leading to a quick switch over. This is especially useful if you use 5 acre meadows, as you can change them all in one go.

For pasture, it really doesn't matter, other than the number of meadows you'll end up having to click on to rotate them to keep fertility up (granted, Argorok's suggestion makes that process pretty quick and fuss-free).

For crops and cattle, it matters -- for that, you want large meadows so you get the larger harvest they give.

Thank you very much to everyone who responded, not only did I get the answer but also some nifty strategies. Locking!