Think about it. If you take profits on every trade you make, you will be profitable. There is no downside to taking profits in terms of preserving and growing your capital.
But yes, of course if you take profits, you are also removing risk. And without risk, there is no reward.
Mining and metal stocks are notoriously volatile. It's a constant process of mining materials and exploring new ventures. For this reason companies get short bursts of bigger profits and then bleed as mining deposits are depleted and no new sources are found.
In my opinion (And Metal Minds), Metals/Mining stocks make great trading stocks. It's important to get in at the right time and exit profitably. However everyone has their own trading style, how long they hold positions, chasing dividends, etc.
In my book, there's no to little harm in taking profits. You can always cash in 25% or 50% of your position and look for new opportunities. Or cash in 100% if you think you've gotten enough from your trade.
For those reasons it's usually good to set profit targets when entering a trade. That way you are not making an emotional trading decision when you are up.