I'd say its much more inefficient as you'd think. Firstly the computations on encrypted data just take a LOT longer, especially for Fully Homomorphic encryptio

I'd say its much more inefficient as you'd think. Firstly the computations on encrypted data just take a LOT longer, especially for Fully Homomorphic encryption. With a single 64 bit addition taking microseconds. Secondly, the FHE code cannot branch based on data. If it could, it would know something about the data, and it wouldn't be proper encryption. This means an if statement becomes "calculate both branches, and throw away the result you don't need". Similarly, a for loop becomes "give me an upper bound of how long this will run", then "loop for exactly the upper bound number of times, if the loop is 'done' early, just throw away the result of the remaining operations". FHE is really cool, and has its uses in situations where you want to cooperate without needing to trust, but it is stupidly inefficient. (Things get really cool if two parties want to cooperate and the computing party can e.g. branch based on their local unencrypted data)