More than you want to know about IB's interest rates is here: https://interactivebrokers.com/en/index.php?f=1595
It depends on the person whether they feel comfortable in having cash positions in multiple currencies in their account or not. I can only speak for myself: I don't care much about having multiple currencies. However, I do care about having to pay debit interest. So I keep a close eye on how much interest IB is charging me for each of the currencies. If I think that I can get a better situation by converting some money from one currency to another then I will do so. But often does the FX commission offset the potential benefits and I just leave things as they are.
It depends on the person whether they feel comfortable in having cash positions in multiple currencies in their account or not. I can only speak for myself: I don't care much about having multiple currencies. However, I do care about having to pay debit interest. So I keep a close eye on how much interest IB is charging me for each of the currencies. If I think that I can get a better situation by converting some money from one currency to another then I will do so. But often does the FX commission offset the potential benefits and I just leave things as they are.