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It's clear that the difference is in the usage of Tenses. And it looks like you can say either of this sentences to convey the same idea. In this regard there is no difference.

Looks like it is a controversial question and I cannot provide you with any more details on that. Did you check my link? It mentions about exceptions.

"Nevertheless, if one simply says, e. g., "...

Pravit, I see that English is your second language, too ;) But you know the rule now.

I have to correct myself now. My first post was not quiet correct (after all, I'm not a native English speaker). There is a rule that you cannot use the Future Tense in the conditional (if-clause)...

I think the shade of meaning is like this:

1. Открой окно, если это поможет тебе уснуть.

vs.

2. Открой окно, если это помогает тебе засыпать. (если тебе так легче спать)