This could apply to any Plone seasoned developer that wants to know more about Volto.
If you haven't done it yet, I recommend you to spend some time to learn about the whole vision and why the community is pushing for making such a thing happen and the reasoning behind it. This vision has been shared by several members of the community during the last few years in conferences and sprints (so if you wish, you can refer to that talks in YT) and as you might know, it has been accepted and agreed by the community that it will be the default user experience and frontend for Plone 6.
After that, as @tmassman pointed out, there are fine trainings (even the full lenght videos from them of last conference), including the new "Mastering Plone 6" which is updated for Volto. I would recommend you to follow with this one.
Learning Volto means quite little compared with learning current Plone stack. Learning ReactJS is usually a good fit and this knowledge can be applied also to other areas/projects not related with Plone/Volto itself.
Check the documentation too:
After this, trying Volto in a small project, or as a side personal project is the best way to compare both classic and new approaches. After you have all these considered and you have to full view, the choosing is yours!
I can imagine a situation in which developers not yet confident to Volto try it out for small projects for training themselves first and continue doing both Volto and Classic projects depending on the type of project, the requirements, etc.
Plone Classic will continue being around, so those that feel super confortable using the classic Plone technologies can continue doing so, you won't be forced to move to Volto.
You'll realise that Volto is specially suitable for projects that require lots of user interactivity and behaviour (so lots of JS on it) or have complex landing pages with a well defined style guide (with blocks that you can model after), allowing users to create these pages by themselves effortlessly. Also it is suitable for websites or intranets that require side mini applications that can be quickly modelled with bare React, integrated effortlessly in Volto. The direct access to the whole ReactJS ecosystem is key here too.
I am aware that some of these requirements can be achieved also with Mosaic and alike, but you'll find that the user experience (and the developer effort to make them happen) after that is much better than Mosaic is able to deliver. Having into account the already existing ecosystem of Volto add-ons and blocks available. Check Volto Awesome too:
In a component based system, everything is a component and can be used across your app, even the view and edit components in a block are bare ReactJS components, no boilerplate required. From zero to all the features that you want a block to have...
As summary, I would say that give it a shot, for the people that we are already sold to Volto is difficult for us not to think that you are going to love it