In general using GrowFX is another great tool to have. There are pros and cons to using it. Biggest of advantages- infinite variations easily editable tree.
I did quick simple, non scientific at all test:
File with 3 growFX-trees.
FileSize: 3MB
Time to open scene: 45sec
RAM required to render: 8.5 GB
Time to render: 3:47
File with same 3 mesh-trees.
FileSize: 390 MB.
Time to open scene: 10sec
RAM required to render: 7.5 GB
Time to render: 3:44