What does M&A banker do?

I'm in IBC in a BB and have been on a few M&A sell side and buysides where so far my experience has had very little (if no) interaction with M&A teams

E.g. structuring on cross border buy side transactions was primarily driven by the coverage team's director (in this case it was a FIG deal) and M&A wasn't involved

So just curious: when does M&A team get involved? How much of the workstreams will they handle (e.g. model, IM, etc? I assume IM and marketing materials will usually go to coverage teams) - or in general, what's the scope of work for M&A bankers?

Thanks