50% salary sacrifice to build up pension pot early - Good idea?

I'm fairly young, no debt, no siginificant outgoings (monthly expendeture of approx £700 including rent). I earn 40k and I want to do a 50% salary sacrifice for 2 years so that I can build my pension up quickly and allow it to compound over the years. I have 10k in savings on top.

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Is this a silly plan? What are some of the drawbacks? (I don't plan to apply for a mortgage for another 5 years so mortgage loan either).