Praefect on Gitaly nodes


I am trying to put an optimal Gitlab HA setup for our company needs using Cloud native approach. Since we need to cut pricing as much as possible - we have one thing left for consideration - Gitaly cluster with Praefect. Gitlab documentation (Configure Gitaly Cluster | GitLab) states that qoute “Praefect should be run on a dedicated node. Do not run Praefect on the application server, or a Gitaly node”.
What are the pitfalls running Praefect on same nodes as Gitaly (this would allow us to cut node count from 6 to 3)?