Many people including me, have 10-15 altcoins and and check their portfolio every 30min to see if there is a change on any coin. So we can make a transaction quickly.
Right now, We are able to see how much profit/loss we made in the last 24h, or since the beginning; However, we cannot see the change rate since the last time we checked our portfolio. In order to do that, they may put a button which resets the current profit/loss rate (and save the current price). Then, 30min later when we re-open the app, we will instantly be able to see, what happened in the last 30 min.
Otherwise In order to see what happened since the last time we checked, We have to check each coin and remember their prices. It can be a bit difficult.
Think that about 15 altcoins, it would be really helpful. So we will not have to remember each coin’s price the last time we checked and instantly see what happened since last check time. So we will not spend much time.
Think about it :)