For example in the sentence: 書くだけでいいですか.
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The meanings are quite similar, but there's a subtle difference.
Both phrases involve settling for something, or one person making a choice on behalf of another:
I think they're different. Look at these two examples:
The first one sounds fine. I'm not sure the second one makes sense.
I think the「で」(in the first example I gave) is used in the same sense as it is in「でいい」. Since it cannot be replaced with「でも」here, I think this is a good way to get an understanding of this usage of「で」. Once you understand that, then you will be able to see the difference between 「でいい」 and 「でもいい」.