Should I use: 'netsh int tcp set global autouninglevel=disabled'

I came across this: 'netsh int tcp set global autouninglevel=disabled'

Should I use it to increase internet speed? What are the drawbacks?

Are you getting close to your ISP's advertised speed? If yes then changing settings isn't likely to help even if not ISP speeds are best effort unless you're on a business plan. You can toggle the setting so if anything happens you can just re-enable it.