As he said, he trade them.

Simplified, trading means you buy one altcoin (on this case, its DASH) when the price is considerably low, and wait for the price increase before selling it back and gain more coin from those price differences. Im still new to trading too, but i believe you'll learn faster by doing it yourself

I do not agree keeping a bitcoin wallet idle is not equivalent to putting your dollars under a mattress. You might have forgot the value appreciation of bitcoin. Dollar is just a currency. But bitcoin is also an Investment.

I just hold them and wait for now, bitcoin investment field is growing and there is no legit company or bitcoin bank currently existing offering interest on saved or kept BTC, trading BTC needs some skills too IMO.

I don't have idle coins! They're for the weak who don't dare invest or trade :3
Idle coins are useless that's the main point. Better invest them somewhere! I don't like to just "hold"

So you mean we have to invest it , I agree with you since that's what I am doing right now but you shouldn't put all your coins in just one basket, its still better to put some coins on idle mode and some on investment. That would be a good way to manage your coins and earning profits as well

i just store it in my wallet and that is it, sometimes if i get a deal i buy with them something digital, but mostly i save it

Having idle coins doesn't mean that its not profiting, the more it is in the wallet the more you earn when you exchange it. As his coins are idle from 2012 he'll earn a good profit. In 2012 he bought and made it idle, but the price variation within 2012-2016 gives profit.

I dont do any thing with my idle coins which are in savings , i do small trading when ever it is i feel that their will be some movement or i do recharge for my mobile and i convert it my fiat currency for my personal expenses. balance i keep for my future

Honestly, it depends on how much coinage you have, IMHO.  If you have a good bit, then I suggest maybe putting them into cold storage or paper wallets.  But honestly, I think the best way to do this and "gain interest" litterally, is to buy some type of physical coin which you can load your coins there.  Something that you can hold on to, and more than likely they will pan out to have a pretty high premium later on down the line in the future when physical bitcoins coming out from this decade will be highly sought after. Better to have coins just sitting in a hot wallet idling, where they could be easily stolen...

Some are on exchanges but most of them are safely stored in my encrypted wallet. It's never safe to store too  on an exchange, but i prefer to have some coins available online for when i get a good deal.
However i never try to have more then 5 btc on 1 exchange.