Best answer by buzz
That said, there is a 35ms latency associated with PLAYBAR, PLAYBASE, and BEAM. In most cases this is a constructive delay because most TV's and cable boxes delay the video slightly. If one needs more audio delay, many TV's offer an adjustment. The SONOS soundbars offer an adjustment too. I have encountered a cable box where the picture leads the audio. This is an impossible situation to deal with because TV's and home audio gear don't offer a variable video delay.
SONOS does not support Dolby Atmos.
The store's installer has a point if one is pushing the TV audio through the SONOS stereo audio players because there is a 75ms audio latency associated with these devices. And, one should not attempt to patch together some SONOS players with the TV's own speakers or an A/V receiver in an effort to build a surround system. The installer might also be thinking about the latency associated with "Grouping" SONOS players with TV sound passing through one of the SONOS sound bars. Here you may have some latency issues, but they can be adjusted with the SONOS bar.
I'm probably an "edge" case and your mileage will vary, but most viewers don't have any complaint with the SONOS sound bars and sync. However, you may encounter an occasional TV program that is uncomfortably out of sync, but this is not a SONOS issue.
I don't know where you are located, I am in the US. From reports I've read, lip sync is better in Europe.