Generally the 〜ばいい has a nuance as follows:
The past version has regret baked into it.
- 行けばよかった: It would have been good if I had left.
Notice the English uses a notoriously hard grammar construction to capture the same idea. Conditional past perfect: would have been good
In the case of the present you can stretch the idea to this:
- 行けばいい: It will have been good if I have left.
I think the hard part is that it’s hard to decide wether to interpret it as present or future tense as Japanese does not mark the future independently from the present like English does. Though in general this construction leands toward being transliterated into the hypothetical future perfect tense: will have been.
Compare to
- 行った方がいい : To leave is(will be) good.
This is a more straightforward and confident perspective.
A Common phrase that uses the ばいい construction is:
- どう言えばいいか: What will have been good to have said.
Overall the idea is that it’s possible to take an action that is bad and you want to avoid the bad possibility. In the past version you regret having taken that path, and in the non-past version you are hoping to not go down the regrettable path.
Keep in mind that these are more transliterations verse true translation. English speakers don’t tend to phrase things like this, but I find it illustrative to use a massaged version of English to explain the idea.
