There are a couple of ways to flag things for follow up.
1) If you want to make sure you go back to a cage/bag on a regular basis you can set a reminder in settings.
2) You can flag any individual bag, group of bags, or an entire line for follow up--and include a note and picture.
Once something is flagged it will have an exclamation mark next to it. If you zoom out you can see the entire farm and where there are flags. If you click into a flagged line/bag you will see why it was flagged. So for example:
1) I want to make sure to check every bag every 21 days. Set a frequency in the Growing Area Activities.
See a flag appear (yellow as it gets close and red as it passes)
Zoomout to see that there are two flags set (the red 2 in the circle)
And see the flags are on lines 5 and 7
You can also set ad-hoc flags at any time while doing any activity. So for example if you are out tumbling and you notice a bunch of barnacles and you want to make sure to follow up set a flag and take a note.
Click into a line or bag to see why it is flagged