Are "beforehand" and "in advance" totally interchangeable? Or are there cases where one of them is more suitable than the other?
In my experience (native American English speaker), the word beforehand is not really used as it is typically defined. I was actually surprised when I looked here and saw "in advance" and "in anticipation" included in the definition. I don't feel those nuances when I hear "beforehand".
I'm actually having a difficult time explaining beforehand simply because it isn't often used in everyday language. I think the best way to understand it is something like: beforehand is a way to avoid using a prepositional phrase. For example, you could state:
I'll finish the report before the meeting.
I'll finish the report beforehand.
They both have the same meaning and I don't detect any significant difference in nuance. However, the second would only be stated if it is clear that you are talking about a meeting (because it was discussed earlier).
Also, I'm not confident if this sensation is shared, but I believe that beforehand sounds slightly lazy (and consequently a little less formal). It sounds like you are sacrificing explicitness and clarity for ease.
In advance is a bit easier to understand. In advance always implies that you are doing something earlier than absolutely necessary.
"Totally" interchangeable, no.
Although in advance and beforehand have similar meanings, one takes complements and the other does not.
In advance of planting, they added fertilizer to the soil.
Beforehand of planting.... ungrammatical
They evacuated in advance of the hurricane.
They evacuated beforehand (of) the hurricane ungrammatical