You might be on heading to avoid weather in a busy environment , where you exercised your emergency authority to avoid weather due to a busy frequency , but still ATC expect you to maintain an initial altitude.
Many scenarios are available . Imagine a dual FMS failure as approach your initial altitude ? Bang ! You will be overshooting
Selection of V/S due to TCAS is another example and many more.
Nothing wrong to follow a VNAV profile , automation is nice but it requires a higher level of vigilence and alertness . And you have to be aware of the non standard scenarios and be ready to react promptly.
Aviation is not black or white , there is no wrong or right way to do it. If VNaV is there it means it can be used but not necessarily.
Regulatory guidance ? I dont think there are any , whether you flew the profile in managed or selected climb , both are correct as long as the result is the same.
As for aviation best practice I would say "stay on the safer side"