i need a new balljoint...

i have a 95 civic dx and when i got new tires on my car they told me i need a new axle and a new balljoint. i knew that i needed a new axle, but i didnt know about the balljoint. i think when the mechanic replaced my axle on that side of the car(the other axle) he might have messed it up. now i know where the balljoint is and have a rough idea on how to replace it, but my question is what does it do and what happens if i dont replace it?

you lose control, crash into a tree, and die.

Yes, balljoints are very important, and not terribly expensive to get replaced. So do it.

They are the movable link that allows your car's suspension and steering to move. Its the joint between the hub and the suspension arm(s), so yep.. its important.

what happens if i dont replace it?
A worn ball joint causes vague and imprecise handling and often unusual wear of components such as tires.

If not replaced, eventually the ball joint will break in two pieces. The steering knuckle will no longer be connected to the control arm.

In other words, that one wheel will flop all over the place, resulting in partial or total loss of steering or vehicle control.

At worst, the wheel will shift rearwards and hit the body, stop spinning and bring your car to a screaming, uncontrolled halt in traffic or cause you to veer off the road or into other traffic.

This is really bad when the other traffic is an 18 wheeler coming towards you at highway speed.

So.........yes, its important to replace worn ball joints.