Portfolio Performance is a section on the dashboard where you can see all the available currencies that you own.

Portfolio Performance or Total Value is written in a denominated price. The value of your portfolio is based on the current market price and then recalculated to EUR/USD for a better understanding of the portfolio performance. 

If the number decreases or increases in the Total Value this does not necessarily mean that you have lost the portion of owned coins but rather indicates that the value of the coins you own has changed. 

My primary wallet is a combined value of all the coins you own. For a better presentation, there is also a graph indicating a denominated price of all your assets on our exchange.