The sequence for me is like an event. It is when I press start on the Mapillary app until I press stop.
If uploading on the website a bunch of images uploaded at once is a sequence.
Sequences have helped when users have requested edits to their image sets by Mapillary administrators when something has gone wrong.
It is similar to a Changeset in OpenStreetMap. You may create and edit content but you save your work in a changeset.
So it is like a container.
When editing uploaded images you can edit your own sequences which could mean editing a bunch of images in bulk from a particular event.
If you have many images to process I see that others here in the forum have used scripts to automate uploading which might be what you are looking for.
When normal viewing sequences are not part of the experience, instead you use the filter to sort images you want to see which may come from different sequences.
If I have explained anything incorrectly I'm sure Mapillary administrators can correct me.