NASA seeks to break the “tyranny of launch” with in-space manufacturing

If your payload is tailored to be launched on one specific launcher - by mass, size, vibration characteristics, orbital inclinations available from the launch pad, etc. - that launch provider finds itself in a monopolistic position.

Often that's not a problem - space exploration started in close cooperation with military which don't have much choice anyway. However more and more the payloads are commercial, or non-profit, and customers could use some competition between launch providers - and, correspondingly, many launch providers would be glad to offer their services to traditional customers of their competitors.

Even more options are available to launch customers if they can split their payload into several smaller parts and use several smaller launchers instead of a single bigger one. Space payloads roughly falls into classes "humans", "expensive hardware" and "bulk materials (most often fuel)". There could be various options dividing a payload for a single mission into several launches. Manufacturing parts in space from material delivered from Earth is a variation of such an approach; assembling spacecraft on ISS by astronauts could be another. In all cases, there could be significant flexibility regarding the launchers used.