I have updated this post in response to comments below and therefore some comments by users below may seem unnecessary. This post was started when Dorico was at version 3.5.
Since one must decide how many flows to use in a project I thought that I would attempt to summarise factors to keep in mind when making that decision. Hopefully I have done this well enough for it to do more help than harm.
Before I do this here is my best attempt to give insight into how Dorico uses flows.
A flow is a collection of adjacent entered music (including potentially any number of empty bars in metred music). Each flow is represented as a box in the bottom panel in Setup mode and is given a default name (Flow 1, Flow 2 etc) but you can name each flow there as you wish.
In a new blank Dorico project in which players have been added there is a single flow which displays staves for each player. If the user enters music without adding additional flows all the music will be added to that single flow. The user can then choose at any point in the music to split entered music into two separate flows and can also add new blank flows. Finally a user can re-order flows as a way of re-arranging their music.
Splitting music in Dorico into two or more flows enables Dorico to complete various operations by selecting one or more flows as the target for the operation. For example one or more flows could be chosen for export. Or an empty flow could be the destination for imported data. Flows also enable the user to quickly locate key points in the music for viewing, editing and playback.
Although flows are used primarily for organisation and operations flows can assist the user with two formatting tasks:
-by default bar numbers restart at bar 1 for each flow. This means that flows are suited to being used to distinguish movements in a score, or numbers in a musical etc.
-flows provide a way of telling Dorico the points in the music at which you wish to automatically generate titles. The titles are automatically generated from flow names.
We may currently rely on only one key fact in deciding whether or not to use more than one flow - that it’s difficult without using more than one flow to add titles at particular points in a project on all layouts. But to answer questions like “Would it be helpful to divide the verses, chorus, bridge etc of a song into separate flows?” we are going to have to understand which features of Dorico Rely on the presence or absence of multiple flows.
Below are a list of factors to consider when deciding whether to use more than one flow in a project.
Factors to Keep in Mind When Deciding Whether to Use More Than One Flow in a Project
-VIEWING, ENTRY, EDITING - it’s possible to quickly access the start of flows for viewing, entry and editing. If instead all of a project’s bars are contained within a single flow all key points in the music (except bar 1) are then located at what will be constantly changing bar numbers - as bars are added and removed.
-PLAYBACK - each flow is a quickly choosable starting point for playback - by using Edit > Go To > Go to Bar or by using the popup list of flows at the top left of the screen in Play mode.
-PAGE ALLOCATION - allocating music to separate flows ensures that by default each flow in a score layout starts on a new page (by default each flow starts in a new frame and each page has by default a single music frame).
-TITLES - Using and naming multiple flows ensures that any titles that we wish to use at the start of flows on all layouts are generated automatically from the names we give to flows (instead of having to enter these titles on each individual layout). If we turn away from using flows to receive this for free we must create frame breaks at every bar which requires a new title to exist above it and then manually enter each and every such title on each and every layout.
BAR NUMBERING -as mentioned above the first bar in each flow is by default bar 1 - but this isn’t a reason to avoid using flows - it can be overridden with Edit > Bar Numbers > Add Bar Number Change.
CAUTIONARY SIGNATURES -it is not possible to show cautionary key signature or time signature changes in the final bar of a flow - the warning bar and the bar in which the change or changes take place must be part of the same flow
EXPORT -the only means of exporting a reimportable subset of a project’s bars for export is to choose particular flows. Graphic slices enable export of particular non-reimportable bars.
IMPORT -a blank new extra flow may be the best way to store data imported to the project either temporarily or permanently
VERSIONS -its easier to use multiple flows instead of multiple projects to make versions of a piece or worksheet - it makes copying and pasting/altered reuse of content between flows.
PS It would be great if Dorico allowed a user to merge two flows. And it would be great if each flow displayed as a box at the bottom of the screen in Setup mode had two tick boxes within that box - one to turn off restarting bar numbers at 1 and one to turn off starting that flow in a new frame (each would be on by default?). These various features would encourage people to use flows for their organisational benefits without fear of repercussions.
PPS I believe it would also be an improvement if there was a conceptual introductory video in the hub. In which concepts like players, instruments, layouts and flows, and the deeper purpose behind each mode (instead of just what happens in each), is introduced.