I had to browse the source of RealBot to get you the answer, but here goes.
All your questions can be answered with the following:
IAD stands for Important Area Definition. (See Iniparser.cpp)
The IAD's are 'important goals' in the map. The documentation is limited, shame on myself; I think they are for assigning 'important areas' so bots will chose these areas as places to go besides the obvious goals such as hostages or bomb spots.
By doing this you can sort of influence their behaviour about moving around the map. Once bots are running around for some time, they tend to get satisfied with some experience and never seem to take alternative routes; by adding important goals / area definitions you can still 'force' the bots to go there.
After looking a bit further, looks like i commented on Important Goals the following:
Code:
// "important goals" should not always be chosen, somehow
// i am not really confident how this works. This seems
// to overrule everything or something. Yikes.
// using ugly RANDOM_LONG to bypass most checks, but still
// keep them in the game
The path_think method will decide where to go, and from all goals (objectives and game goals) the highest score is best candidate to go to.
The IAD code seems to be bugged; so if you add them, chance is that bots will not plant bombs as often (or not at all).
In short, if you don't add them, you're fine ;-)
Dang, i should compile this thing and clean it up...