When using ODK to collect geographic evidence of work being done in the field, GPS speed can be a useful tool to ensure that the submission is plausible.
For example, conducting vaccination should be done with a movement speed at or near zero. Conducting community messaging via megaphone might occur at a walking pace. Tracing a path or boundary may occur at a bicycle or motorbike pace.
If Geopoint or Geotrace features included GPS speed, it would be easy to set a range of acceptable speeds to filter out submissions that occurred while moving too fast or too slow to plausibly have done the work correctly.