Left bundle branch block is a pathway for electrical impulses that originate from a sinus node in the right atrium. The left bundle branch pathways provide conduction of the electrical impulses down the septum (wall separates the right and left heart chambers). Left bundle branch are pathways for impulses to contract the left venrtricle (pumping phase). There is a right side BB for contraction of the right side. Both chambers are timed to contract at the same time. A LBBB could delay the contraction of the left ventricle as there will be another activation impulse from another source usually the right ventricle.
There shouldn't be any problems associated with LBBB if the right branch stays intact. Anyway the presence of LBBB indicates that various parts of the heart muscle are not supplied with blood very well. LBBB without CAD is indirect evidence there has been a small infract, or heart attack sometime in the past. Usually an infarct is a result of CAD.
CAD damages the vessels due to insufficient supply of blood to an area and heart cells die (necrosis). But there can be other causes for heart cell damage. It can be a virus, bacteria, alcohol, medication, drugs, etc.
Hope this provides some insight to your question, and if you have any further quesitons or comments you are welcome to respond. Take care