Apps which make use of the Playdate's capacity to serve as a sound generator, custom clock face, screensaver decoration and/or other passive/semi-passive tools, trinkets and toys are hampered by the inability to customise auto screen-lock options from the user settings menu.
Some examples of such apps:
- Weird Alarm Clocks
- (Seen a few screens saver apps eg. DVD bouncing logo)
- Cloudburst
- Productivity Rabbit
- Bad Apple!! For Playdate
- P.O.S.D
I know there is an option to keep the screen on while charging (sometimes) and I am not sure if there is documentation available as to how or if developers could enable this on their end. I don't have much software and development knowledge myself, however I did notice this impacting my use of the device and restricting my enjoyment.
I think this would be a feature that can help build on established fundamentals and further empower playdate developers to do even more useful or weird and wacky things. 
I have checked in the settings and searched online but I couldn't find a way to control the auto screen-lock settings myself, other than what has already been stated above. I am not sure if maybe that feature does actually exist? So maybe I'm wrong to post, but as I could not find a conclusive answer, I was motivated to bring up this request!
The examples above are provided to illustrate app types that benefit from screen-on function; I haven't played all of them and cannot comment on if all of them don't have this functionality. However I played and noticed this feature in P.O.S.D, a neat tool that generates different types of ambient noise. Unfortunately the screen switches off and sound mutes after a short amount of time making the app as-is currently unsuitable for long-term passive-use creating custom soundscapes.
(Even if this functionality can be hard-coded in by dev's, adding this feature would still make the Playdate as a whole more flexible and accessible for general users!)
Sorry if this is in the wrong place - I am still learning but was all the same motivated to post as I think this feature would be a very powerful upgrade! 
