Bots in custom games were removed
Bots in custom games allowed me to test things like champions, items, masteries, AI, etc... in a controlled environment without interference from other players. I saw a post asking about the range of CoC (it's 1000), and wanted to check it in a custom, but could not, since the option was removed.
Bots not only allow experimentation, but could also give a challenge. Load into a custom versus Malphite, Garen, Cassiopeia, Zyra, and Leona. More oppressive than Doom Bots. But if bots are coming to sandbox mode, it's all good.