not having to maintain a list of features+icon yourself (if you want to do that; some batch script could convert the monochrome icons in iD to the style of icons you use)
localized feature names
When editing/adding POIs:
search by localized name
terms for features with which one can find them (e.g. find shop=pet when typing "dog")
a list of fields (e.g. phone, website, ... on POI features) which one could display for the user to fill out
for the fields, further information by what kind of UI they should be selected (e.g. is it a color, is it a multi-select etc...)
See https://github.com/openstreetmap/id-tagging-schema (+ https://github.com/osmlab/name-suggestion-index/)
When you use the presets, you gain
When editing/adding POIs: