Riverside is useful because it combines several parts of a night out in a relatively small area. Restaurants, bars and late-night venues are close enough that you can change direction without restarting the evening.
Why stay nearby?
If nightlife is a major part of your trip, staying close to Riverside reduces unnecessary transport and makes spontaneous plans easier.
Street 136 connection
Street 136 sits within easy reach of Riverside and is one of the established nightlife streets visitors often explore during the evening.
When to go out
Phnom Penh nightlife tends to build later in the evening. Starting with dinner and moving into bars and clubs afterwards usually creates a more natural pace.