As per my understanding , UL quality is measured using SNR only if there is no SRS configured. In this case only SNR is choice to measure UL quality.
SRS is not configured due to many reason. It is depends on the eNB. Pros is SRS is not there hence only option is SNR based measurement.
Cons is if there is no UE transmission due to various reason and eNB detects SNR leads to mis calculation.