Session VWAP is the default version of vwap on most platforms. It answers one question: what is the average price everyone has paid today, weighted by size. Institutions are measured against it, which gives it a real mechanical role rather than a purely chartist one.
Intraday traders use it as the day's dividing line. Price above it means buyers who bought today are on average in profit; repeated rejection from below is read as a market in control of sellers.
It is heavily weighted toward early-session activity as the day progresses, so late in the day it moves very little and stops being a useful dynamic level. For context that spans multiple days, use anchored-vwap anchored to a meaningful event instead.
Related: vwap, anchored-vwap, volume-weighted-moving-average, session-breaks, initial-balance