what is the different between Grant-PnPAzureADAppSitePermission and Set-PnPAzureADAppSitePermission

[mvcsharepointdev]

I have this script (from this url https://techwizard.cloud/2022/03/20/sharepoint-and-graph-api-app-only-permissions-for-selected-sites/) to provide access to selected site for our Azure Active directory :-

$siteUrl = “SiteURL”

$clientId = “6d83d654-4e58-4477-a157-f9bf635eeffc” #clientid of app you just registered

$certThumbprint = “47C45F47E0E17AD419709713B3BE864A5A7190DC” #App with Sites.Selected permission

$tenant = “tcs.onmicrosoft.com”

Connect-PnPOnline -Url $siteUrl -Interactive

$writeperm = Grant-PnPAzureADAppSitePermission -Permissions “Write” -Site $siteUrl -AppId $clientId -DisplayName “PowerShell-SharepointOnline”

$PermissionId = Get-PnPAzureADAppSitePermission -AppIdentity $clientId

Set-PnPAzureADAppSitePermission -Site $siteurl -PermissionId $(($PermissionId).Id) -Permissions “FullControl”

now i am a bit confused on what is the different between Grant-PnPAzureADAppSitePermission and Set-PnPAzureADAppSitePermission? Can anyone advice?
Thanks