Why might using Kinetex C8 be more beneficial than using a C18 column?

Very hydrophobic molecules can be difficult to elute from a C18 phase. A C8 column will offer very similar selectivity, but less retention allowing for elution under moderate conditions. An additional benefit is that due to the smaller ligand size of the C8 phase,  bonded phase density is higher than for a C18 column. This increase in bonded phase density can aid in giving enhanced peak shapes for difficult to analyse compounds.