System designers have a choice in the use of directional couplers, tappers or unequal splitters in the "main spine" of a DAS.
The directivity of the directional coupler in theory reduces interference between signals on the return path, however since the signals are so small on the return path the effect is generally small. The return loss of the coupled port is generally good which simplifies system modeling. Microlab has a wide range of directional couplers from the low cost CK-66 series to the high performance CK-10 series.
Tappers are generally less expensive, are very rugged and have broad bandwidths. The negative of the tapper is the lack of isolation and poor VSWR on the coupled port, but once again these factors may not be critical to the overall system performance. The DK-x8 series are typical tappers.