Spending Bitcoin helps in the economics of Bitcoin industry.  It enables the exchange of hands which attracts Bitcoin adoption.  It balances the price of Bitcoin in terms of supply and demand making it less volatile.  Hoarding Bitcoin can artificially increase Bitcoin price due to the premise of scarcity but hoarding also means dumping in some point where it crashes Bitcoin price, regular practice of hoarding and dumping makes the Bitcoin market highly volatile and may discourage merchants and other entity to engage in Bitcoin market.  So spending Bitcoin can also help in merchant adoption.

These are some of the good effect of spending Bitcoin.  As we all know, Bitcoin is created with an original intention to be a currency where it can be used for purchases and not to be hoarded and be a speculative asset.