HUDs give you some information, but it heavily depends on how many hands you've played with a specific opponent.

Some stats, like VPIP(voluntary put in pot %) and PFR (Preflop raise %) are gathered comparitively quickly, and give you basic information that you can use to form a general idea of you opponent's playstyle. Other stats like 3bet% and AF(aggression factor) are gathered a bit more slowly but give you more information about how aggressive/passive your opponent is.
There's quite a few stats, and you can tailor your HUD how you like.

I take notes about EVERYTHING. I keep my head in the game and stay focused, and not let myself be distracted. It's amazing how much information you can gain from a single showdown.

Huds are good for general information but having good detailed notes is what is going to separate you from the 10 tabling reg.

Espically note the following
Does he raise or just call with nut flush draw/baby flush draws (most regs will raise with nut flush draws and call with baby flush draws)
Does he bluff/raise flop with overcards/top pair
What hands does he stab at pot with when you check turn
what hands does he stab at pot when you check flop
does he value bet thin as in will he bet 3 sts with QJ on Jxxxxx board
What does he call cbets with - if middle pair pocket pairs then you must double barrel more
what does he 4bet get it in with in CO/Bu v Blinds
Does he cbet/give up aka one barrel monkey

I could go on for ever .. Basically this is the online version of having a live read. Therefore for example after a lot of hands if some one shoves allin on a wet flop and you have a note which says he only calls with nut flush draws, then you know he in more likely has a set or two pair and therefore your overpair is no good and must fold

The biggest boost to your bankroll will be when you keepa close eye on how the fish at the table plays. Most fish will stab at a pot if you show weakness. You must determine what range of hands he stabs with and then used this to trap and/or to value bet to death.. poker is easy when you have reads...

I would nearly go as far to say that I will fold to aggresssion on turn and river without a read. These are the streets where you make all your money in cash games so having reads/notes is essential