Bitcoin's appreciation is directly proportional to alt coins. However many people hold altcoins for two reasons; In fact, people use cryptocurrencies for two specific reasons:
1. To hodl as a store of value for long term gains.
2. As a tradable asset, to increase one's investment portfolio.

More so, we have seen in many cases where Bitcoin does a bullrun and leaves altcoins behind. Usually, in this instance, the alt coins begin to show a red indicator - reduction in value, this is because of the gap between them. In the mean time the altcoins will play catch-up.

So generally, BTC is like the base pair for all altcoins. But as the market continues to mature we would see many more pairs like in the traditional capital/Forex market. But for now depending on what exchange you are trading on, you could have ***/BTC, ***/ETH, ***/USDT, ***/USD, and ***/BNB.