Do you tip your food delivery riders or grab drivers? Why or why not?

I do if they deliver food when it's raining or go the extra mile to provide great service. Hold the same perspective too -- if it makes their day at a small expense, why not! I always purchase the Grab vouchers from Shopee and that often saves me at least a $1, so why not just pay-it-forward :)

No. It is a very brief interaction. Also, it's customary to tip in other places but in return, the staff are very motivated to provide the best dining experience. That's not always the case in Singapore.