The ability to design the CapNMR probe using a consistent sample containment geometry (the NMR flowcell) that does not change with each introduction of a new sample provides a geometry where the RF detection coil can be tightly coupled to the sample.  Contrary to tube-based approaches, where the RF coil must be somewhat larger than the tube to permit mechanical clearance for removal and re-insertion of a new tube for each new sample over the course of thousands of sample changes, the microflow approach used with CapNMR probes facilitates winding the coil directly onto the NMR flowcell (for high fill factor), and the use of an extremely thin capillary wall that would not survive the mechanical rigor of the robotic, tube removal and re-insertion approach.  Further, the coil and flowcell geometry can be designed so that the RF field produced by the coil captures a maximal amount of the flowcell (and sample) volume (for high observe factor).  Together, these attributes result in optimal signal detection from your sample, and greater S/N.