Registering a building obligation for a garage - advantages / disadvantages?

Hello everyone,
our planning/design includes a garage complex (9.2 x 6m) right on the immediate property boundary to the neighbor. The planner mentioned something about a building encumbrance needing to be registered on the neighbor's property... Further statement: "...if the building were shorter, no registration of the building encumbrance would be necessary..."

What exactly does this mean, and what are the advantages or disadvantages here?

Effort and work for 20cm means that. And the neighbor has to agree to the garage. Even more work and effort.

Simply plan 20cm shorter and that’s it.

That means there is a magical limit regarding the length? Is that stated in the [Landesbauordnung]? Suppose one plans 9m and the bricklayers accidentally make it 9.2m?

Surely it is stated somewhere, whether in the state building code or the development plan, etc... your planner seems to be aware of it.

A wall certainly does not become 20cm too long by accident. In the worst case, demolition, correction, or even dismantling is threatened.

I get along quite well with the neighbor to whom the garages are supposed to belong. What official steps would need to be taken if I build more than >9m and what costs would arise?

The architect takes money, the building authority too, maybe even the neighbor because of restrictions on the buildability of his property.