I understand that initial encryption costs a lot, that can be one-off though. My question was more about the computation on data - whether the same computation

I understand that initial encryption costs a lot, that can be one-off though. My question was more about the computation on data - whether the same computation (using this library?) on homomorphically encrypted data is performing as well as on unencrypted data? Is there a penalty to pay on every operation after initial encryption?