Soft Dollars

I’m failing to see the link between soft dollars and agency/principal trades.

If I direct a borker/dealer to buy/sell a security, the broker/dealer might execute this instruction as either an agent or principal depending on whether they go in search of the security or sell it from their own stock respectively. But this is just trade execution and nothing to do with soft dollars.

What’s the link to soft dollars? Soft dollars from what I’m reading is you overpaying for trade execution but getting an additional service in the form of research. But why would I want this research if I’m calling up a broker and directing him to buy/sell. Bit too late for that isn’t it? I’m asking for a trade to be carried out so the research is useless to me at this point.

And then is there a distinction between a fund manager managing money on behalf of clients and an individual calling up for trade execution?