I have a client that is running FileMaker Server 12 and they would prefer to stick with it and only upgrade their desktop clients and their mobile users to FMP and FMGO 13.
Anything that is typically executed by Server. The obvious one is "perform script on server", but also any ExecuteSQL() calls you make that would use the new FETCH and OFFSET functionality.
In general avoid using any new functions. When the server can not evaluate it, the client will and that can cause slowdowns.
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