A LOG field, when added a layer, allows your crews to keep a running history of maintenance or other notes associated with individual features. A LOG field displays on a layer's feature form just like any other field but with a button titled "Add/View Notes". When you click this button the historic log is expanded to full screen where you can scroll through the past notes or add a new note. Any newly added notes are automatically stamped with the date and time and your email address. By design, previously entered notes cannot be altered by anyone. This gives you confidence in the integrity of the log. If an error is made on an entry then you can submit a new note describing the correction.
See the non-editor exception settings on the Layer Settings screen which allows users who don't have edit permission on a layer to still be able to log notes
Adding Notes On Layers maintained in another GIS system
If you wish to add notes to a layer that is edited in another GIS system and periodically re-imported into this map, then you need to read the special "keep attachments and notes" instructions in the Import Shapefile topic.