Andy is the most knowledgeable guy I've seen on the web when it comes to repairs.
In this set of vids. I have to disagree, these are not spider cracks but rather structural cracks. IMHO, spider cracks are tiny cracks that appear with no apparent stress source. Seems to be one of these things that just happen. I have had to repair spider cracks on my toe rail which is a solid massive slab of FG running the length of the boat :
No way that thing is subject to undo stress.
I have not seen any indication of failure in any of the spider cracks I have repaired using the simple, painless, reasonably clean method shown in post #6. For the heavier repairs which Andy is demonstrating yes, go deep and add additional layers of cloth for extra strength.