A Service Item Source is needed because time in ConnectWise PSA can't be transferred over to QuickBooks Online unless it is an item. This setting determines how you would like the item to be named when it gets to QuickBooks Online. We recommend it go over using one of the GL Account options.
Work Role-Work Type:
A Work Role is a role that drives billing rates (Engineer, Project Manager) 
A Work Type alters billing rates like after hours or travel.
If this was used to create an item in QuickBooks Online the item would end up being "Solution Developer-On-Site" or "Consultant-Remote"
Please note that the GL account that is used the first time when this item is created in QuickBooks Online will ALWAYS be used in the future. So, if the GL account changes in ConnectWise PSA for that item, it will still show up in QuickBooks Online as the original items GL entry.
This option should only be chosen if your GL Accounts are set with the Work Roles and Work Types and will not change.
Work Role:
A Work Role is a role that drives billing rates (Engineer, Project Manager)
In this case the invoice item in QuickBooks Online would be "Consultant"
Please note that the GL account that is used the first time when this item is created in QuickBooks Online will ALWAYS be used in the future. So, if the GL account changes in ConnectWise PSA for that item, it will still show up in QuickBooks as the original items GL entry. This option should only be chosen if your GL Accounts are set with the Work Roles and will not change.
Work Type
A Work Type alters billing rates like after hours or travel.
In this case the invoice item in QuickBooks would be "Remote"
Please note that the GL account that is used the first time when this item is created in QuickBooks will ALWAYS be used in the future. So, if the GL account changes in ConnectWise PSA for that item, it will still show up in QuickBoos as the original items GL entry. This option should only be chosen if your GL Accounts are set with the Work Roles and will not change.
Service-GL Account
This names the service entry based on the GL Account and puts the word "Service-" in front of the GL Account Number so it could be GL Account Number "Professional Services" or "Remote Work". It would show up in QuickBooks as "Services-Professional Services."
GL Account
This will just name the item with the GL Account. So if you had a time invoice that had the GL Account Number that was named "Professional Services" it would name the item in QuickBooks "Professional Services."