Altcoins are the best source to earn huge profits because when a new altcoin launches, it usually pumped over 100%, with few exceptions. You can earn a profit in a limited time frame. Furthermore, the technology they are using and the innovation they are providing to the market is top-notch. Some are very good projects in terms of technology, for example, ETH, SOLANA, DOGE, XRP, etc.
Altcoins being used mostly for speculation purpose. The fact that if altcoin is also having another usefulness like give native coin user a cheap way to send their money. I remind you how expensive the bitcoin and ethereum transactions are. That's why altcoin gives alternative way for people to send or receive their money with lesser fees compared used native blockchain like bitcoin or ethereum.