Microsoft's import tool can bring over a whole Google account in a few clicks, and the temptation is to take everything. The problem is that some settings don't mean the same thing on Bing. A tCPA learned on Google's conversion volume gets imported as-is, but Bing's audience pool is smaller and skews older and more desktop-heavy, so a target that worked on Google can starve delivery there.
Keywords, match types and negative lists usually transfer fine. Bid strategies and audience layers are where I'd rebuild by hand. A good rule of thumb is to import keywords and ad copy, then set bidding fresh with Maximize Clicks or manual CPC and let Microsoft's own data build up before moving to a target. Has anyone seen an imported tCPA hold up without a reset?