Before I got a cycling computer I used my phone on a quad lock. Wasn't worried about rain too much as it was waterproof. I did get burn in on the screen from long sunny rides, which affected the value depreciation of the phone. Plus if you get stuck somewhere and your phone dies, you're screwed. Computer just added in extra independent resiliency and is easier to use on bike.
Before I got a cycling computer I used my phone on a quad lock. Wasn't worried about rain too much as it was waterproof. I did get burn in on the screen from long sunny rides, which affected the value depreciation of the phone. Plus if you get stuck somewhere and your phone dies, you're screwed. Computer just added in extra independent resiliency and is easier to use on bike.