Diamond Block is an extremely strong block. It has 84 hitpoints (none of the other blocks exceed 50 hitpoints), which means it can resist the damaging weather (everything except Meteors), and you won't need a Field Generator.
For example, a Diamond Block will survive 6 consecutive hits from Cosmic Blasts weather (12 block damage). Because 1) blocks regenerate their health over time, 2) there is a limit on "how many projectiles can the weather cause", 3) it's highly unlikely that even 2 consecutive blasts will hit exactly the same spot, it makes Diamond Blocks practically impenetrable.
It can also survive 3 hits from Master Manipulator, which is good for players who are worried about accidental misclicks on their base (especially if their base is on a Gas Giant or above the core ocean).
You can make Diamond Blocks even stronger by using the Material Mod Placer to add Densinium Ore to them (hitpoints of the ore are added to hitpoints of the block, and Densinium Ore has 62 hitpoints, so resulting health will be 84+62=146 hitpoints).
Things that can destroy Diamond Blocks
Meteors (they deal 1000 damage. No block except Dead Core can possibly survive that)
Explosion below the defeated Gas Bag (whenever this monster is destroyed or captured, it emits a devastating blast directed downwards. This is strong enough to destroy a Diamond Block)
Fun facts
Diamond Block is somehow a valid soil for crops. It still needs to be tilled with a Hoe.
Precious Metal Construction (Craftsmanship tree).