Hi Yingjie Guo,
Yes this is necessary ! if there are two tiles ! there UUID shouldn't match otherwise they will conflict . And If you are creating it, through Nitrous it updates that file automatically.
Thanks for your information. I am still confusing. For example, I use jive-sdk create a table tile and list tile, I will get the definition.json file, but I can't find id property in both tile list and tile table.