Does Svg Need Viewbox. Without viewBox attribute it has value equal to 0 0 width height. It defines how all the lengths and coordinates used inside the SVG should be scaled to fit the total space available.
Here is some practical information that I find useful to understand and particularly to work with SVG viewPort and viewBox. The viewPort the SVG tag itself is like a container that the SVG image is. The numbers separated by whitespace andor a comma which specify a rectangle in user space which is mapped to the bounds of the viewport established for the associated SVG element not the browser viewport.
The viewBox is inside the viewPort.
The actual size of your SVG may also be called viewport. In SVG however there is only one coordinate system by default used to position elements inside the viewport. The viewPort the SVG tag itself is like a container that the SVG image is. And so when an element needs to be positioned inside an SVG it is positioned relative to the entire SVG viewport.