Wait For Update and other debug counters

[burner]

I try figure out that why my factory A) lags and B) have huge lag spikes. It feels that when lag starts it is hard to get it end. I usual need put game.speed to 0.2 or 0.1 for some time that it will end.
What is "Wait For Update" at debug? It will go to 200 when that starts.

I have tried to convert my factory to robots from belts but looks that it go to even worse.

Do someone know that is there many to many calculations at botnet logistics? I mean that If I have large botnets do cpu usage grow at exponent when you add boxes? So at perspective of cpu use Is it better to make lot of small nets and transfer things with boxes/trains or use large nets?