Linking things like your Tumblr, Email, etc. makes it easier to find your accounts on other platforms instead of searching up your username
Adding additional pages to your site can make it more fun and interactive, along with feeling more organized
You can add links to media you enjoy as well. Links to music you like, a video you enjoy, a content creator you follow, etc.
Most people know links as these blue or purple underlined bits of text, like this, but something like this also counts as a link. they are very customizable and buttons are basically just decorated links. you can have fun with the shape, color, outline, etc. you can even make images into links if you want, links can look pretty much however you want.