Webroot and Windows Defender

On Windows 8 and Windows 10, Windows Defender will automatically get disabled if another antivirus is present.
 
Running any additional products is really a personal preference. I don't feel like you'll see any real performance difference by running Windows Defender, but that's something you can test yourself.
 
Hope these links help:
How to disable and configure Windows Defender on Windows Server 2016 using PowerShell
How to permanently disable Windows Defender on Windows 10

You can leave Webroot do to its real time scanning, and let Defender run periodic scans (not real time). Different models / engines / tagets ; should be beneficial, yes?
 
Windows 10 Anniversary Update upwards
 
see here for details:
https://www.tenforums.com/tutorials/51514-turn-off-limited-periodic-scanning-windows-10-a.html

IMHO... Running multiple active antivirus scanners is both redundant and often causes severe degredation of system performance. If you are looking for multiple tiers of protects then use multiple layers. Add spam filtering / antivirus scanning on the email server, add a DNS filter / antivirus to the router and if possible setup software restrictions on the workstations via Group Policy.

@
 
yes, running two AVs that do the same thing would be 99.9% redundant.
 
With Defender running in 'classic AV' mode (periodically), and Webroot doing it's live good/bad/monitoring thing, you're combining two approaches, at different times.