What are Issues of Transforming Robots or Robots that Combine into Bigger Mechs?

[The Colonel]

There's also issues like the requirement for massive engineering redundancy in any single transforming vehicle as mechanical loads change between forms. This goes up by another exponent if you then assemble the vehicle into a load bearing part of something else.
Also, the most important part of most vehicles is the pilot - if you assemble five vehicles into one, you've got four guys sat their like drunken monkeys whilst the fifth does all the work.