Android Boot loop causes Greeting fellow enthusiasts

My daughter(device) is an asus zenfone c. And She has already been rooted. The other day, i've downloaded a game which tell me that the game can't be played on a rooted device. But before I proceed on de-rooting my daughter. I've been warned by the de-rooting software provider that playing with root access could cause boot loop. 

And now here i am wondering "what is the connection in playing with root and boot loop?" So what i want to ask is. Can anyone told me what thing i should and shouldn't do to avoid boot loop.

Thank you in advance and sorry for bad english and not pinpointing my question
There are a lot of causes ! You don't need to have a list of thing can causes boot loop. Better is need to prepare a nice plan and check everything is ok before do something risky. Must to know : read root/flash guide entire before play with a device.