This has been a debated topic over the years. Approximately 20 years ago, research was done to answer the question. At that time, it was shown that lag bolts hold just as well as "through bolts" in live tree limbs.
Trees are not merely wood objects but living things, which do react to events that happen to them. The research showed that living trees do react to the foreign object (bolt) by tightening the tissues around it. There are several theories about what actually happens internally in the wood, but the research showed that a lag bolt holds on average equally as well as a through bolt in live branch tissue. The results were the opposite on lumber, which is dead wood, not living tissue.
Also, Dr. Shigo, University of New Hamshire, a very well respected research scientist of arboriculture, demonstrated that a "through bolt" sometimes causes a decay tunnel completely through a branch, eventually making the branch weak and prone to failure, In his work, the lag bolt , which was less invasive in that it fit tighter (or made better contact with the internal
wood) and did not introduce wound openings on two sides of the limb, but only one side. The result was that the lag bolt was less likely to have internal decay over time.
In my experience, I have seen lag bolts used for cabling in the past 25-30 years. I have yet to see one fail. I have seen many cables, which were installed in the thirties and forties, break, but in most cases it was the cable that broke, not the bolt.
The cables used today are lighter, stronger, and last much longer.
