Performance issues can arise by various factors/reasons.
Some known performance bottlenecks are:
1 – Number of direct children. If a node has more than two to three thousand direct children it may impact performance.
2 – Real Time Validations. If there are many real time validations that include complex or recursive formula properties then you will see performance issues
3 – Number of properties with defined values per node. When each node has a large number of values this can use up memory and can cause the system to page to virtual memory depending on the server setup
will add up more as and when it comes up on my mind.