SpaceX recently posted a side-by-side comparison of their version 1.5 raptor engine and their version 2.0 raptor engine. The 2.0 raptor engine is a complete redesign to remove complexity and reduce part count.
On the left is version 1.5 and on the right is version 2.0.
So clearly removing part counts and components provides advantages of reduced size and reduced complexity. Reduced complexity and parts means less seals, joints, and points of failure. The importance of reducing this type of complexity can be seen in the highly complex space launch system (SLS) which continues to run into problems just filling up with fuel and test firing due to valves, seals, and debris from assembly.
SpaceX also redesigned the raptor engine because they need more rapid manufacturing times for these engines because thirty are needed for each starship to launch. Reducing complexity can decrease manufacturing times but that is never a certainty. Here are some of the likely pros and cons from what we know about the redesign.
Pro:
Better supply chain (less parts, less inventory, better quality control)
Fewer points of failure
Possibly shorter assembly line (less points along the line)
Size reduction (continuity tends to be cleaner than joints)
Con:
Longer times at each point on the assembly line
More skilled labor (the redesign replaced part joints with welds)
Inconsistent tolerances (an issue that was eventually fixed when applying the same principles to the Starship main body)
In summary, by replacing parts with welds a manufacturer is replacing low-skilled assemblers with high-skilled welders. Even skilled welders will also need to be trained on the particular parts in order to get consistency. Fortunately this can mean less inventory as more value add is done directly on the assembly line. In fact, far more can be done within the factory rather than relying on pre-assembly and sub-assemblies. It seems that SpaceX was able to use these changes to also reduce assembly time and maintain a quality product (engines are test fired). These are great outcomes given the more generalized Pros and Cons above.