Joe,

The operating temperature of the piping results in thermal expansion of the piping system. The gaps are required at guides and line stops to keep the expansion stresses to reasonable values by letting the piping to expand freely, until the restraint then becomes effective for restraining the dynamic loads. If you change all the gaps to zero, then it is likely to exceed the allowable expansion stress by over-constraining the piping, as well as having huge loads at some of the zero gap restraints.

The design of the restraints for dynamics is different than for the sustained or thermal expansion cases. I would call it 'boxing in' the piping. First, the piping is configured with enough flexibility for thermal expansion, with initial restraints selected and located to carry weight for the sustained stresses. Second, the pipe runs are evaluated for restraint of slug loads by including a line stop / guide in each change of direction. Some longer runs might need additional guides. Some short runs could have enough restraint from nearby line stop / guide. All line stops / guides could require some gap unless it is located a point of neutral thermal expansion. It would be a more complicated piping geometry to make it flexible enough for thermal expansion using all zero gap guides and line stops. The design for dynamics restraint involves a balance of flexibility for thermal expansion and of stiffness for avoiding vibration response to the dynamics loads.