You would line bore for 5 reasons: Spun main bearing, insufficient crush gap, out of alignment main bearnigs, just an out of round main bearing hole, or if you bought new caps or somebody pulled the old ones and forgot where they went. The process involves milling the main bearing cap and block slightly. Then, the mains are installed and bored to their proper dimension. It's expensive, so I wouldn't buy a block that needs it. A line hone doesn't require the cap be milled, and cleans up minor damage or misalignment.