Motion is the key to Puka Nacua's success
As Sports Illustrated's Conor Orr detailed, "the Rams utilize presnap motion more than any team in the NFL, save for the Miami Dolphins." The tendency showed up "on 21 of 66 snaps" against the New Orleans Saints in Week 16, when Nacua "gained 107 scrimmage yards" on motion plays, according to Next Gen Stats.
No. 17 helped himself to nine catches for 164 yards and a touchdown against the Saints. It was one of seven 100-yard games during a 1,486-yard campaign.
Keeping Nacua on the move not only forces defenses to show their cards. Trail Nacua and it's sure to be man coverage. Stand pat and it's likely zone. Setting up coverage to double Nacua is also harder when he moved around so often.
There are other advantages, like hiding Nacua behind other receivers.
Nacua adds more to the Rams offense than one more set of hands
Perhaps one of the less appreciated attributes brought to the LA Rams offense is the sheer range of qualities that Puka Nacua brings to the LA Rams offense. One trait that has truly endeared him to the Rams offense, and to HC Sean McVay especially is his willingness to block for his teammates, even if his blocking assignment is bigger and more powerful than he is:
The willingness for Nacua to place a helmet on another helmet has infused a great deal of upside into the Rams base 11-personnel offensive package. With Nacua blocking nearly as effectively as a tight end, the Rams can add and opt for more plays that simply cannot be considered without solid edge blocking.
But it also opens up the Rams offense to use bunch formations, or placing two or three receivers in close proximity to one another, which allows the Rams to confuse defensive backs and leverage mismatches: