When a qubit is measured in a quantum computer, it undergoes a process called "wave function collapse" or "state reduction." This collapse causes the qubit to take on a definite value, either 0 or 1, with a probability determined by the superposition of the qubit's quantum state before measurement.
If all qubits in a quantum computer are measured, the resulting system effectively loses its quantum properties, and it behaves like a classical computer. The quantum parallelism and interference effects that make quantum computers powerful are no longer present, and the computational capabilities are limited to those of classical computing.
In a sense, you can think of a quantum computer without any qubits in superposition as a classical computer, capable of performing classical computations. The advantage of quantum computing lies in harnessing the power of superposition, entanglement, and quantum interference to perform computations that would be infeasible or inefficient on classical computers.
Therefore, if all qubits in a quantum computer are continuously measured and prevented from undergoing quantum operations, the system effectively behaves like a classical computer, and the advantages of quantum computing are not utilized.