About its need and its usage, see below an nmrML extract (generated by the JAVA nmrML converter, dev. beta version) ;
Moreover, in this same extract, see how I tried to solve the spectral referencing issue, thus following the Philippe's advice suggesting to use the CHEBI ontology.
<softwareList>
<software id="ID00005" version="Version 2.1" cvRef="NMRCV" accession="NMR:1400215" name="Bruker TopSpin software"/>
<software id="ID00103" cvRef="NMRCV" accession="NMR:1400135" name="spectrum post-processing software"/>
</softwareList>
...
<referenceableParamGroupList>
<referenceableParamGroup id="ID00104">
<cvParam cvRef="NMRCV" accession="NMR:1000014" name="solvent suppression"/>
<userParam name="Method" value="range"/>
</referenceableParamGroup>
<referenceableParamGroup id="ID00105">
<cvParam cvRef="NMRCV" accession="NMR:1400074" name="baseline correction"/>
<userParam name="Method" value="Automatic baseline recognition"/>
</referenceableParamGroup>
<referenceableParamGroup id="ID00106">
<cvParam cvRef="NMRCV" accession="NMR:1400XXX" name="group time delay compensation"/>
<userParam name="group time delay" value="72" unitAccession="UO_0000189" unitName="count unit" unitCvRef="UO"/>
</referenceableParamGroup>
<referenceableParamGroup id="ID00107">
<cvParam cvRef="NMRCV" accession="NMR:1000075" name="spectral referencing"/>
<userParam name="ppm" value="5.23" unitAccession="UO_0000169" unitName="parts per million" unitCvRef="UO"/>
<userParam name="Reference Compound" value="" unitAccession="CHEBI:17234" unitName="glucose" unitCvRef="CHEBI"/>
</referenceableParamGroup>
</referenceableParamGroupList>
...
<dataProcessingList>
<dataProcessing id="ID00108">
<processingMethod order="1" softwareRef="ID00103">
<referenceableParamGroupRef ref="ID00104"/>
<referenceableParamGroupRef ref="ID00105"/>
<referenceableParamGroupRef ref="ID00106"/>
<referenceableParamGroupRef ref="ID00107"/>
<cvParam cvRef="NMRCV" accession="NMR:1000071" name="phase correction"/>
<cvParam cvRef="NMRCV" accession="NMR:1400044" name="fourier transformation"/>
</processingMethod>
</dataProcessing>
</dataProcessingList>
...
<spectrum defaultDataProcessingRef="ID00108">
<spectrum1D>
<processingSoftwareRefList>
<softwareRef ref="ID00103"/>
</processingSoftwareRefList>
...
</spectrum1D>
</spectrum>