Tying contracts were at the heart of the 1998 FTC suit against Microsoft. Presumably, by including a copy of Internet Explorer with Microsoft's OS, competitors would be crowded out of the market. I won't comment on the prescience of the Justice Department (as astute readers will surely be able to handle that task on their own) but I will comment that the presumptive logic behind this part of antitrust legislation is deeply rooted in Euvoluntary Exchange.
The idea is something like this: consumers want product X and are willing to pay a fair price for it. Producers also want to sell product Y, but they can't move it because it's naff. So instead of selling products X and Y separately at their respective prices, they sell X and Y together, coercing consumers (by circumstance, mind you) to accept a product (product Y) they otherwise wouldn't have done at too high a price. Producers can get away with this only when they have sufficient "market power" (in other words, the BATNA to buying their product is quite unattractive indeed). That seems to be the rough-and-dirty of the theory. In practice, the Sherman and Clayton Acts are often used as special-interest bludgeons that punish successful (read: good at serving the customer) firms, particularly foreign-held entities (like Alcan).
For some of our younger readers, there used to be a time when music was purchased in small bundles, called variously at times LPs, cassettes, 8-tracks or CDs. Other formats existed, but the notion of buying one song at a time was fairly rare. Sure, there were 45 rpm records with two or three songs pressed on them, but for the most part, folks bought the entire long format album (imagine Sony's despair if they had to make a Walkman using a 45). Isn't this a tying contract? In order to get "Here Comes the Sun", you also had to buy a copy of "Octopus's Garden". Why did nobody ever take Ringo to court? You could say that The Beatles (or their record label) had plenty of market power.
Antitrust as she is writ is meant to ensure distributive fairness. Antitrust as she is practiced stifles the vigor of innovation. Its discretion and caprice mark what Robert Higgs calls regime uncertainty. Approach with caution.