Great question, I think the answer is quite simple as well!
RFI only includes the
hands you open when action is folded to you, or opening UTG. First aggressor.
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A high RFI could indicate a player is opening too wide, and this player could be very easily exploited through using a wide 3bet range.
While a low RFI could be interpreted as a nit who has a tight range and usually both are quite well tied with the players VPIP.
PFR includes opens/3bets/4bets
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A high PFR could indicate a player who is 3bet/4betting too wide and could be exploited through aggressive 4/5bets
A low PFR usually indicates a passive/weak opponent (calling stations, limpers) These are players you can aggressively attack with the top of your range
Some tips for using these on a HUD would be to also check the players 3bet/4bet frequencies when they have a strange looking PFR, to see if this can be exploited.
And for RFI, take a look at what positions they are opening the most from, if they are opening 11/12 from the BU, you may be able to exploit this by aggressively 3betting some less than normal holdings, but remember to also check their F3bet(fold to 3bet) in these positions. But generally if they are opening this much from LP, you will be able to exploit this by 3betting large with a large portion of your range.
Hope this answer helps in some ways. Thanks for your post.
