Firms new to Revit tend to continue to do early design phases in CAD, and then switch to Revit in DD.
"Revit is too slow for quick concept stuff."
"It's faster and saves budget to do it in CAD first."
"We'll just import into Revit when we're ready to switch."
This is natural, but misguided.
If you start in CAD, you have to set it up in CAD.
Then when you switch, you will have to set it up in Revit.
And then you will have to 'import' or trace all your CAD work in Revit (this is not a trivial task).
Can your project budget absorb two setups? Do you like throwing away profit? Then ignore this.
CAD is faster in concepts/SD when you are faster at CAD than you are at Revit, and have tight CAD templates and standards.
Revit is faster in concepts/SD when you are faster at Revit than CAD, and have tight Revit templates and standards.
Do you think in five years you will be doing many CAD projects? If not, you should get fast at Revit as soon as possible, and you should invest in tight Revit templates and standards as quickly as possible.
Don't drag it out. Start once.
(Also, there are some cool things that Revit and other BIM tools can do for you in concepts/early design that CAD can't. You won't learn about these if you aren't using Revit early.)