For me, it came to reliability. Got tired of a new consumer router every year or two, because they would need to be reset often, act strange, or simply die. Not acceptable when working from home.
Tons of other nice-to-have things, like better logging and network mapping, separate guest SSIDs...features that one may not need, but great if you do.
The biggest feature is the ability to add and change APs as much as i want, no limits. Only 3 now, but they all behave, and roaming between APs is seamless and invisible to users. Just last week I did some firmware updates to APs. I rebooted one while an ATV client was streaming. No stutter, no pause, next AP picked up the ATV and it never knew the primary AP was off line. Slick.
To be fair, the gap has closed between consumer and enterprise gear. IMHO, entry-level UBNT gear sits right in the sweet spot between the two. There are surely others that fit the bill, but UBNT has been around long enough to have mature firmware, and I have the most experiecnce with them.