We think it is nice that users have the choice to try new features early. But you can ask the question whether it is the best solution to leave it up to the users to decide whether or not to try out new features.
It might not always be the best solution, especially if they leverage a (centralized) IT support organization which may not (yet) be able to support new capabilities (or even be aware of them). Although it wouldn’t be a huge problem per se, it might generate some unwarranted calls to the support staff.
Luckily, Microsoft learned from earlier mistakes and is providing the ability to control the presence of this toggle through the OWA Mailbox Policy assigned to the user.
A suggestion would be to update the default OWA Mailbox Policy to disable the toggle by default and create a new policy and assign it to a (small) group of test users (e.g. the ones enabled for Targeted Release) who could take advantage of the option.
That way you limit the exposure in your environment and keep it available to users best suited to evaluate new experiences which will be coming to everyone else when it’s released more widely, later.
To update the OWA Mailbox Policy, connect to Exchange Online Powershell and run the following command:
Set-OwaMailboxPolicy “<OWA Mailbox Policy Name>” -OutlookBetaToggleEnabled $false
Unfortunately, there is no “OutlookBetaToggleEnabled”-parameter for the New-OwaMailboxPolicy cmdlet. Therefore, you’ll have to create a new policy, and update it afterwards should you require a separate policy for some users that would be allowed to take advantage of this feature.