Bounce all your VSTi's to audio eventually, once your sure youve got the arrangement how you want it. Also a good tip is to use plugins on standalone audio files by right clicking on the file then choosing the plugin fx from the list, this way you get the effect but dont use the CPU at all.

If i have a vsti which i know i need to edit again but need to bouce it down for the CPU's sake i usually render to audio then save as a different cubase file so whenever i need to get the changed arrangement i can load up the previous file and render.