You are asking very strange question. Base64 is for encoding a binary data while .svg is just a file type for vector graphics for the web in a simple HTML-like style.

I even will copy a direct definition of Base64 from Wikipedia (or Wikiwand extension in my case which adds awesome UI to Wikipedia).

So Base64 is a group of similar binary-to-text encoding schemes that represent binary data in an ASCII string format. You can encode any data you want to Base64: text, styles, images, including svg. Historically it was invented for email attachements to support them on any machines and protocols. Today it is used to inline small assets into HTML to avoid a lot of extra HTTP requests. Answer here from historical point of view is very long and I will just leave these two good answers on StackOverflow:

1. Why is base64 needed (aka why can't I just email a binary file)?
2. Why do we use Base64?

The difference is that the base64 is inline, which means the browser won't have to fetch one extra asset (the same reason why you concatenate CSS and JS into one file each).