Here is what can be done in order to Improve the performance if there is a model which is already built and you want to improve the performance of the model.
1. Try doing Pareto Analysis of the model. Pick top 5 modules of your model and see if you can optimize line items of these modules by changing the Summary of each line item. You also may want to look at the Dimensionality of each line item and see if you have got it right for each line item . For example if you are working on a multi dimensional module and you want to refer the parent of one of the dimension that line can be carved out and put it into separate module called system module.
2. Take the blueprint of the model and look for multiple IF ELSE statements. If you have got more than two IF ELSE conditions within a line item I would recommend breaking these and look for alternate solutions. Looksups are really helpful. Also avoid using TEXT and TEXT Joins as much as possible
3. Try to reduce the number of properties within a list and replace properties as line items in a module. There are a few exceptions where you will have to have a property like when are using Assign function, Display Name for a Numbered list, Using properties to open new dashboard etc
4. Check the user concurrency of the model. Sometimes it so happens that user concurrency takes a toll on the model performance and you have got to very careful and plan for this at the beginning of the project. However you can still go ahead and request Anaplan to perform this test for you. Note: It is a paid service.
This is the illustrative and not exhaustive list.
Anaplan's engine is very powerful and at the same time flexible enough to let you do whatever you want to do. But we follow some guidelines in order not to degrade the performance of Anaplan. It all boils down to one thing and that is how are we designing the model (PLANS) and most importantly how are we building it (DISCO)