# How much is modest in this case for the usefulness of two-way fixed effects?

Regarding the usefulness of two-way fixed effect (TWFE), Guido Imbens mentioned that TWFE can be good starting point for DiD if the N and T are modest, I am wondering is there any criteria for "modest", how much is modest here?

From this Chaisemartin, 2020, slide 2

However, TWFE can be an attractive model for baseline (control) outcomes when N & T are modest" but not exible for large dimensions.

• Guido Imbens (Sargan Lecture, RES 2021).