It's a client specific general setting, so the options menu is the right place to configure it.
If (and only if) the rain effect heavily drains on resources even on high profile video gear (Something I cannot test since I don't own such hardware), then I'd agree it should be disabled by default. Otherwise I'd say it's perfectly normal that you get all effects which do not cause errors by default, and can then choose to disable some if your hardware doesn't match up.