The European platform allows traders to write options without having to put the entire underlying asset up as collateral. For example, you might write a call for 1 BTC, but only need to deposit .15 BTC initially. This enables traders to make the most of their capital, particularly in allowing traders to hedge or speculate without tying up all of their assets. Efficiency doesn’t come without risk: if a position moves against the trader’s expectation, and they are unable to put up the required collateral to maintain it, that position may be liquidated. Keep an eye on your positions, and make sure your portfolio is able to meet its collateral requirements!