What automatic does best
Discovery. Auto campaigns surface real shopper search terms you can then promote or block. They are low-effort to launch and ideal early on.
What manual does best
Control. Once you know which terms convert, a manual campaign lets you set the bid per keyword and match type, concentrating budget where it pays. This is where ACoS comes down.
Use them together
Run auto to keep discovering, harvest its winners into manual, and add its losers as negatives so the two do not compete. Coordinating them by hand is fiddly — AIAdKing manages both in one nightly cycle so they reinforce rather than cannibalize.