cause you are taking everything apart and putting new ball joints in so it is possible that the alignment angles will change. we normally do alignments on cars at work after we do anything like this.
To make more money for your employer? Unless your truck was aligned with your ball joints severly worn out, there should be no need to realign it.
I didn't even take my spindle off. Popped the old lower joint out, put new one in. Couple hours both sides.
Rent the ball joint press, makes life easier. I don't like whacking away at my suspension with a BFH for hours, makes me sleep uneasy at night.