Good question! If you want to hold your EOS tokens or several other tokens issued on EOS blockchain in your own wallet, then you will need an EOS account. To login and interact with carious Dapps on EOS, you need your own account too.

Think like if you hold some ETH or ERC-20 tokens, you create a metamask or MyEtherWallet acccounts on Ethereum chain. Similarly, on EOS, you should have your own EOS wallet instead of entrusting centralized exchanges. Once you have your own account, you can also vote for EOS BPs.