Dear Deewendra, I am by no means a guru but I’ll attempt to answer. I use helpers in templates until it starts to look contrived (i.e. too many nested subexpressions, especially with Ember Truth Helpers). Defining a computed property for every single line of logic in a template also seems like an abuse to me.
Lauren Tan recently gave a wonderful talk at EmberConf: EmberConf 2016: Idiomatic Ember: Sweet Spot of Performance and Productivity by Lauren Elizabeth Tan - YouTube where she talks about this (helpers starts around minute 22).