Voltage Divider: Given the high resistance value, $R_3$ might act as part of a voltage divider network. This can be used to step down a voltage level to a desired value for other parts of the circuit.

Biasing: It might also play a role in transistor biasing for $Q_2$. By setting the base voltage in a specific range, it ensures that the transistor operates in the desired region (cut-off, active, or saturation).

Current Limiting: $R_3$ may also act to limit the current flowing through the circuit, especially through $Q_2$. High resistance would reduce the current, protecting the transistor from excessive current which could cause damage.

Load Resistor: In some configurations, a resistor could be used as a load resistor which drops voltage when current flows through it, thus creating a measurable voltage difference across it that is useful in certain applications like amplifiers.