Today, people create flows that need dozens or even hundreds of stages, but if you try to combine all of these actions into one flow, it may be challenging to manage and keep that flow going.
By eliminating flows with hundreds of steps, you may manage flows easily by using child flows. This method is very useful if you wish to reuse jobs across a cloud flow or even between different flows.
Consider a scenario in which you have a child flow and you want to add or modify a contact in Dataverse based on the name of that contact.
https://docs.microsoft.com/en-us/power-automate/create-child-flows