In this photo, you can see some attempted repairs on this chimney flashing. The decking boards are a little soft around it, indicating that there has been some leakage over the years here. It can be so tricky to correct because of the low slope

In these photos, you can see that spray sealant has been applied to random and targeted areas in an attempt to avoid or stop leaks in the past.  This would be a temporary fix at best

The drip edge helps protect the wood underneath the shingles on the edge of the roof. It is installed on the eaves and is a big plus.