Summerlin South sits on the western edge of the valley, which means it's the farthest major community from the airport, the Strip, and the east side of the valley. If you work downtown or on the east side, your commute from Summerlin can be 30–45 minutes in normal traffic.
For people who work in the northwest valley, near Summerlin itself, or who work from home, the location is ideal. For everyone else, the commute is the primary trade-off for living here.
The 215 beltway provides reasonable access to the rest of the valley, and the I-215/US-95 interchange is a key commute node. But Summerlin is genuinely on the western edge — that's part of what makes it feel removed from the city, and part of what makes commuting challenging.