Could some one can explain, in pratical, what is the difference about indoor and outdoor placement in ap configuration?
In some countries the regulatory rules applicable to a Wi-Fi AP depend on whether it is installed indoors or outdoors. So, for instance, there may be channels that are indoors-only or a higher tx power may be allowed outdoors. The placement setting determines which of these two sets of rules are used on the AP for countries where this is applicable.
what is we have network with both indoor and outdoor AP's? Which settings do we choose in that case?
You'll need to create two diffferent AP groups and set the placement appropriately for each.
“In some countries”… does this indoor/outdoor setting have an impact in the US?
For US, Tx power for Indoor placement is less than Outdoor placement.