Pardon, but most modern Mac (that include MacBook Pro) are capable on dual channel memory. So long you install a match pair the dual channel will be in use. This is also why those model with soldered on-board memory, you will see two DIMM on system report instead of a single large DIMM.

Here's the spec sheet from intel, you will see "Max memory channel: 2"
https://ark.intel.com/products/67355/Intel-...o-3_10-GHz-rPGA

While Apple did not mention dual channel but they do advice owner to fill both slots with equal memory. https://support.apple.com/en-us/ht201165

Here's some healthy discussion on Mac & dual channel memory. https://apple.stackexchange.com/questions/1...al-channel-mode