It's how quickly I can jump from notifications to thread, or to profile, or how fast I can scroll feed without jitter etc. it's hard to quantify, but all other clients (that I try) are noticeably less smooth/fast. Primal is by far the slowest, nostur is a bit janky, yaki is aight, but a lil clunky imo, and Damus feels as fast as Twitter (when it's not crashing...so 90% of the time).