Saving daily data for each user - MySQL
Definitely save new day data only if something has changed.
Now the question is onr table with data , or types and data.
Depends on number of columns and the periodicity of change.
For two table, there is a higher overhead, but iwth single wide table (lets say 10 or more types or data), you will be storing lot of duplicate data. In addition, more joins will be needed.
I would say single table is better if storage is not an issue