Shearing and/or size selection of CUT&RUN-enriched DNA is NOT required nor recommended for several reasons:
The output of CUT&RUN is mainly mononucleosome-sized DNA fragments, making it unneccessary to shear DNA.
CUT&RUN DNA yields are very low (vs. ChIP). Additional shearing and size selection risks loss of target-enriched DNA.
During CUT&RUN library prep, there is a clean-up step to remove adapter dimers. This step will also help to retain CUT&RUN-specific fragments.
The library prep PCR parameters specifically amplify adapter-ligated fragments from 200-700 bp, eliminating larger DNA fragments from the library.
Large fragments generated by CUT&RUN and observed in final libraries are typically nonspecific background. Shearing DNA at earlier steps would include them in library prep, diluting on-target signal and increasing background.