Yes, there’s a difference between sending tags together versus separately. Here are some points:
Each connection requires a “slot”. When you send them separately, each one of those sends counts as a slot. Older PLCs can make few connections, so you may quickly run out of messages you can send.
This also matters in high speed applications where you process a single packet. When you send a single UDT bundle, you receive it as a single piece of data you can then process. In high speed communication, it can become different as timestamps of the messages will be different if they’re individually created.
Generally speaking the above isn’t critical in most cases, but where you need highly reliable data it does become a factor.
Hope that helps…