These inputs evolved from an instrument input and electric guitars don't have balanced connectors.
As a mobile device it's great to connect the guitar and bass during a jam session.
The two XLR inputs are balanced inputs, everything is in the unit.

Yes agreed, and the headphones out also double as a line 3/4 out with identical quality as the balanced outs 1/2!

It seems I didn't make myself very clear, so I'll ask again.
One of the differences between balanced and unbalanced audio connection is that a balanced connection has less risk for unwanted noise and usually has a bigger maximum output/input level. From this point of view unbalanced Ins are inferior to balanced. So, my question is why Babyface Pro FS has unbalanced TS 3-4 Ins instead of balanced TRS? Is this because of:
– cutting production costs?
– technical limitations?
– general idea, according to which the constructors decided that it was unnecessary?
– another reason?

Well, that does not explain, why 3-4 is not also ballanced (beside unballanced).... It could have been ballanced as well as inputs 3/4 in UCX are....

Maybe that it is because of easier standalone use, or whatewer....

The question was, what reasoning was behind BBF design that 2/3 cannot be also ballanced.

So, far we do not know, we just guess. Only RME could answer that question....

You take my question too personally and draw conclusions that are too far-reaching. My intention was not to offend you. The only constructive and relevant response to my question that was given in this thread concerned power consumption limitations. Could you elaborate on how balanced inputs increase power consumption? If indeed this is the case, it might be the answer to my question.

To all those who have discussed the properties of balanced and unbalanced connections: could you please write about the advantage of using unbalanced inputs over balanced ones? Because if there is no such advantage, all the information you provide is off-topic.

True, in the UCX and similar interfaces there are balanced inputs which also work for instruments with unbalanced connections.
To be honest I also asked myself why there are unbalanced inputs on the Babyface pro. But I simply assumed it’s more simple to construct such a circuit or whatever. For my personal needs (external mic pres on inputs 3/4) it always worked absolutely fine so far. That’s also the reason why I did kind of 'defense the unbalanced connection' above. There are so many people thinking a balanced connection delivers the better quality per se. It doesn’t.

I think there's nothing wrong with being curious about why a certain product is designed the way it is. I find it simply interesting. There are other aspects of Babyface that have been explained on this forum, such as why there are no dynamic processors (to reduce production costs and make BF more affordable for customers, as well as for power consumption reasons) or why the ports are placed on different sides (to maintain a compact size for portability reasons). I've learned something new each time.
In my second post, I provided possible reasons for the unbalanced 3-4 inputs. You also mentioned several reasons, such as cost-cutting (keeping BF "entry-level" for customers) and reducing power consumption (due to technical limitations). I just hope someone can provide a more definitive answer, and it doesn't necessarily have to come from an RME representative. However, the answer of "it is like it is, and if you don't like it, just don't buy it" is not a satisfactory response for me. Anyway, thank you for all the information you've provided and for your effort.

Compare with other products on the market. When doing consulting in other forums I always told the people to avoid interfaces that are only bus powered, because in all cases there were issues, that the headphone outputs were not powerful enough for many people.

The usual market has then usually only products that work either bus powered (with such limitations) or need a power supply.
RME designed here an exceptional device that can work USB bus powered, has still enough volume on the headphone amps and can optionally be equipped with PSU and has more useful features compared to the products of other companies.

I, personally, regard the BBF Pro FS as the sweet spot of what is possible for such a bus powered mobile device.

Its balancing in terms of design with circuits, features, to have a "round product" and also with costs.

With the features, you have in mind, I would estimate that the device would be in the range of over €950.
And this would not be to the benefit of users. It's a mobile and entry-level device, giving you everything that you need for mobility and use cases that most people have.

It sounds to me that you are still very sceptical, but believe me, if everything would be that easy, then the BBF Pro would have all those features. Look at other USB bus-powered devices of the competition and compare the features … Maybe then you could agree more with what I say.

Why?