The default behaviour when a user clicks on a lookup field in Dynamics 365, is that it opens the record in the same window. In some scenarios this behaviour is not ideal since users may want to open related lookup records in another window to view more information to assist in populating fields in the current record or make decisions.
Quick view forms can display fields from the related record, but this would involve customization to the quick view form every time a new field needs to be displayed.
An alternative to this, is by using a Web Resource that opens the related lookup record in a new form behaving like CRM 2011. This simple Web Resource is ideal for scenario’s where the lookup field is re-populated, since the web resource is in a read-only state and only changes if the source lookup control changes value.
Repeat steps 6. and 7. if you want to apply the window popup behavior against another lookup field. The only changes you would make is the label and custom parameter which would be set to the lookups field name.
So, to conclude this simple Web Resource is a good solution to resolve scenario where users would need to view another related record for more information to assist in populating data or decision making.