Constraint Solver in SV (Topic: Randomization)

What is the need of Constraint solver? What will be the difference if i am using below code without line “solve x before y”.

class ABC;
rand bit x;
rand bit [1:0]y;
constraint c
{
y inside{[x:3]};
solve x before y;
}
endclass

Read 18.5.10 in SV-2012 LRM you will find the answer there. :)