The Amalgam is the raider's choice of ships. But it's also rather a good miner in it's own right, with a strong mining laser from even tier one, and more importantly at higher tiers the ability to reach deep space. This makes it invaluable in your early deep space days of having another miner that can get there.
What makes the Amalgam such a good raider? If you attack a base, it will take a percentage of that base's cargo. As the ship levels up, that percentage gets higher. AND that percentage is on top of the normal cargo capacity of the ship, which means that you can carry way more than your normal full cargo.
Enter how many resources your target base has and what level(not tier, but level) your amalgam is versus your max cargo on your biggest miner. This will determine when you should use the Amalgam or your miner.