The summary table in the Bayesian SEM window will be updated whenever the number of MCMC observations is a multiple of the value specified here. For example, if you specify "1000" then the summary table will be updated when the number of observations reaches 1000, then again when it reaches 2000, and so on.
This setting affects the updating of the Bayesian SEM window, but not other windows. The posterior summaries for Additional Estimands can only be updated by clicking in the Additional Estimands window. The same goes for posterior summaries in the Custom Estimands window.