This is a very complex issue, to the point where Yanmar
requires all their saildrives to be bonded and Volvo
will void your warranty if you bonded their drives.
There is much misinformation on this thread (as there is in every other thread on this topic), a lot of it caused by the incorrect use of terms .... grounding, grounded, bonding and electrolysis
or even interchanging terms such as grounding and bonding which are two entirely different things.
A far better use of your time is to learn from a reputable source. I highly recommend the Boat Owners Guide to Corrosion
by Everett Collier. Or google
"Ed Sherman Corrosion", Ed has a number of excellent articles on line and he has the credibility of ABYC and BoatUs behind him.