First off, great question @bookworm86.
I also agree with @silversea_starsong and @rangertreaty50. Currently I only have a few casual observations but they were significant (to me) in that they occurred in places where there is a slim chance that I will get back to and I did not get a chance to photograph them because of dense foliage and light. I have just returned from a trip where I had an overwhelming (for me) number of observations and although I may have recorded photographically 90% I still wish to note the other 10% that avoided my camera capture. As well, I have observations that I made prior to me recording by camera and they are part of my life list of fauna - I know I saw them, I want a record, I know they are not verifiable (and in this case I’m not concerned), and iNat is the best place for me to record a comprehensive list.
@kueda stated in one post, https://forum.inaturalist.org/t/records-on-inat-that-are-of-no-value-because-theyre-not-identifiable/4062/5, “iNaturalist is a platform for helping to connect people to nature first, and a database second. If iNat caused these people to slow down for a second and pay attention to a non-human organism when they might not have otherwise, then these observations have value.”
In this post he also stated, " the data iNat produces is a byproduct."
My casual observations occur as a result of me connecting to nature.
There are other casual observations where the organisms are not wild. Sometimes this can be the best chance to collect a definitive image. I first chanced on iNaturalist when I was scouring EOL and the Map of Life looking for definitive images to help support my attempts to identify different organisms. I continue to use the images on iNaturalist to define my identifications - if the defining image is that of something not wild, so be it, it may well help me identify something that is wild.
Other instances of casual are when images are not supported by a date or location. I know I have loaded scanned photographs from back in the day and the exact date of observation is unknown - I would be lucky with a year. And sometimes the location is fuzzy - was that in Jasper National Park or Banff? Yet for me these observations are significant because they add to the back story of my own personal journey.
I’m sure I’m missing something.
[edit: I knew it would come to me, I saw a Javan Surili in a certain place, on a certain date, and no photo. At this time there are only 20 obs. of this species. Even though it is not research grade it has research value - someone knows a spot where they can go and possibly have a verifiable sighting.]