If you are spending dollars, you're not buying BTC with those bucks, so your are also spending Bitcoin. ¯\_(ツ)_/¯

bitcoin and fiat is "value". Spending either of those reduces your savings. If you choose to save in Bitcoin, you either sell your bitcoins to spend fiat or you spend your bitcoins. It's splitting hair to say those are different. The less you spend the more bitcoins your can save.