Geometry optimizations are achieved by two ways:

First by using path relative commands instead of absolute commands and converting lines to paths.

Second by reducing the number of decimals.

The size reduction can be significant.

Style optimizations group properties assigned by attributes or inline (eg stroke=".." or style="stroke:..") into CSS classes.

CSS classes are computed to factorize properties between more than one element.

The last option, moving attribute properties to inline, is more a syntax convenient than a size optimization.

Text optimizations are achieved by removing empty texts between items and also comments.

These are useful when the SVG is hand written.