I thought the idea has always been to hold!
It is okay to do so, but the thing is, if you have bitcoin as an investment, trying not to develop the attitude of always spending it will help you a lot, and if you know buying something like a pizza will make you become used to spending your investments on similar unimportant things, then maybe you can avoid it.
No! No! No! 
Investing in BTC is a good idea, but it's also not a bad idea to try to make Bitcoin circulate. Bitcoin isn't a stock which is not meant to pay for something. Bitcoin's value grows if the network of those accepting it as something valuable increases. With every purchase, you contribute to increase this kind of circulation, and you thus help the network effect.
But how to avoid to lose money if your purchase "too" much? First, of course, if you have a business yourself, of any size, you can accept Bitcoin, so the BTC you lose due to spending trickle in.
If you don't have that possibility - still no problem: re-buy the BTC.
There is an interesting article here about network effects in Bitcoin and how they have shaped its history and preserved its leadership, with some examples not known to that many people, like the network effect as the driver of the successful resolution of the conflict regarding Segwit in 2017, or the importance of "Bitcoin only" companies. It shows how the "store of value" concept and the "payment" concept complement each other.