It's actually extremely common for quantum algorithms to have measurement operations halfway through. But they apply to individual qubits, not the whole system.

It's actually extremely common for quantum algorithms to have measurement operations halfway through. But they apply to individual qubits, not the whole system. For example, error corrected quantum computation involves continuously measuring particular stabilizers in order to catch when they flip. Another example: measurement can reduce the cost of uncomputation (e.g. [1]). [1]: https://quantum-journal.org/papers/q-2018-06-18-74/ https://quantum-journal.org/papers/q-2018-06-18-74/