I have just recently looked at two mechanical projects in which the notes on the plumbing plans make the plumbing contractor responsible for painting not only the piping but patching and painting walls from demolition of plumbing fixtures! I have never understood why architects and engineers throw other trades into a different division.
Another common example I see is including some roofing as part of the mechanical scope. The mechanical contractor will be responsible for patching the roof on mechanical related items, yet there are numerous other penetrations that will need to be patched. On top of that, the specifications will then state that the roof is under warranty and only ABC contractor is allowed to perform any work on the roofing.
Typically the subcontractor will just exclude these other trades, but that just makes an additional headache for the general contractor trying to compare bids.
These situations can also create problems for the owner once the project is complete. For example, who should the owner call if the roof is leaking when two different roofers patched penetrations? This situation creates the perfect game of point the finger.
Oh by the way… To me, it would make more sense to make each trade responsible for their respective trade only. This may make it a little tougher during the design, since a broad note for the additional work can’t be used but I think the end result would be much better.