"Internal sell-side" Equity Research

Have been told that working in Equity Research at a place like Fidelity International (this is different from Fidelity Investments / FMR in the US) is like working as a sell-side ER ("internal sell-side"), even though FI is buy-side. You belong to the internal pool of ER that the PMs managing funds will come to consult on the names you cover, as opposed to being part of a PM team and generating investment ideas.

Just wondering if anyone has more insight or experience to share on this regard. More broadly, how working in the ER or (public) investment departments of different large buy-side AM (e.g. BlackRock) and smaller investment firms are like. TIA