Aligning staff with changing customer and store needs is key to store operations management. There is considerable research on personnel scheduling, but little on the common phenomenon of Real-Time Labour Allocation (RTLA), where mismatches between workforce supply and demand are addressed by allocating potentially cross-trained employees in real time. Our interviews with retail practitioners confirm that RTLA decisions lack analytical justification. In view of this, we design a generalisable stylised Retail Store Simulator (RSS) and instantiate the RSS using data from a gourmet supermarket. Simulation results show substantial long-term benefits to store performance from RTLA – a potential 6.6% increase in market share compared with No-RTLA. We further discuss RTLA's benefits under various employee cross-training configurations, answering a question from the collaborating retailer – “given the benefits of RTLA, how should we manage workforce flexibility?” We conduct extensive “what-if” analysis and find that broadening employee skill range and deepening employee proficiency increase the benefits of RTLA. This research helps understand workforce management at the execution stage.