In SPIR-V, local variables inside functions are loaded (with OpLoad) and stored (with OpStore). In WGSL, however, the semantics of "load" is lost. For example:

var x = 1.0;
const y = x * x + x + 1;

This would translate to 3 OpLoad instructions for x instead of one. It would be unfortunate to recommend people to have temporary const variables, since nothing visually indicates whether an access to something is an actual operation, or just a use of an SSA value.
One way to address this would be to have a syntax for "load" of a variable, e.g. *x.
Another way is to rely on drivers doing this optimization, if they always do.