There is 3 types of risks while botting:
1. Detection - this is always "above us", no matter what you bot, as long as you are attached.
2. Player reports - all the public activities (not solo instanced) are in risk, competitive PvP games and repeated farming in high-populated zones (Like Felblight in Tanaan) are in highest risk possible.
3. Server-side heuristics - here the instance farming take place - no matter if you are running Cata raids weekly or 24/7 HoL/Botanica - your bots are examined by the server side mechanisms to recognize "botting behavior":
Generally speaking nowadays the risk is considered low enough for some farming like Cata raids, and it is very high for other activities like HoL 24/7 farming, but consider the fact, that on single wow license Cata farming could be minor activity if ran on single toon, but when you draw the pattern to run them 10 times a week from 10 toons, every week - its risk is uprising!
No one on these forums could safely give you the exact number "howmuch" risky this is, but please, do follow the common botting rule: "Dont bot on account, you fear to loose!"