Once the latest transaction of a coin is buried under enough blocks, fully spent transactions that preceded it can be discarded to save disk space. To facilitate this without breaking the block's hash, transactions are hashed in a Merkle tree, with only the root included in the block's hash. Old blocks can then be compacted by stubbing off branches of the tree. The interior hashes need not be stored.
While these calculations are accurate for archived transactions, the load on recent and 'active' blocks is significant. The bitcoin network is restricted to a rate of 7 transactions per second, to prevent the network from unsustainable expansion. In comparison, the VISA network handles an average 2,000 transactions per second, with daily bursts of over 4,000 transactions and up to 10,000 during seasonal peaks. If the bitcoin network transaction cap was removed, and the network load was similar to that of VISA's (2000 TPS), each client (and miner) would require a constant download and upload rate of upwards of 1 megabyte per second, and each 10-minute block would be over 500MB.