> informal networks in the company

Not just smokers. The little groups who would go and leave for a walk and coffee. The people who ate lunch together either going out, or together in the kitchen.

These were opportunities to cross the boundaries of your department and role, it was a great excuse to make friends in other groups, and gain insights.

For me the first ones I tried to align with were always in CS and Accounting. The former often had great insight into emerging issues (next weeks "bug", next months "project"). The latter had insight into how the business was really doing, hearing from the people who looked at your "raw" numbers could tell you more than any company meeting where "everything is great".

Working from home killed these, and "zoom" or "slack" are not the same - people are far more guarded when they understand that the company owns that communication channel, that it is recorded/monitored.