Normally this problem probably won't even get noticed by the user, but I've just added a relationship to 1200 recordings at once and noticed my RAM utilization climbing up by approximately 7GB!
The RAM utilization starts to climb after hitting the Done button and triggers several warnings of my Browser (most recent version of Firefox) because the action takes over a minute to complete. After it has finished, the relationship pop-up dialog disappears and the RAM utilization drops to its previous level almost immediately.
Of course such a huge amount of edits caused 504 errors on submitting, so I decided to split the addition of relationships into three batches of 400 recordings each. Thus I found out that the RAM utilization is not only dependent of the number of relationships that are added per batch but also of the existing releationships (or maybe the position of the affected recordings?): The third batch of changes to the last 400 recordings took almost 5GB of RAM.