Is it important to add 4% PhiX as indicated in https://developer.illumina.com/news-updates/singleron-gexscope-single-cell-rna-seq-data-now-available-on-illumina-basespace-sequence-hub?

PhiX is added for two main reasons: to ensure the heterogeneity of sequenced bases during the run and as a means of obtaining QC metrics during the run. Since we are sequencing transcriptomes, we have no problems with the heterogeneity of sequenced regions and, technically, the PhiX is not necessary. However, we recommend including a PhiX spike-in as a measure of the quality of the run (if 4% is too much, this can be reduced to 1%).