Refocus, first of all, is an almost worthless action.
From the sage advice supplemental pages of the PHB 2nd edition:
"About the only time refocus isn't a foolish thing to do is when you've got absolutely nothing useful to do anyway."
This is not entirely correct, because if you use the rules in the DMG for characters entering an already-ongoing fight, it might turn out to be useful to have a high initiative. However, those rules are kinda stupid, so I wouldn't use them.
Second of all, I'd recommend your group move to a fully cyclical initiative system (if you haven't), in which you ignore the negative limits for Delays, and in which you basically ignore initiative scores once they have been used to determine action order. Refocus then ceases to exist.
Thirdly, to answer your question, I'll use an example.
Suppose there are three people fighting, A, B, and C. Here's what they roll in total for initiative.
A - 21 (initiative bonus +1)
B - 12 (initiative bonus +4)
C - 4 (initiative bonus +3)
The normal sequence of actions will be:
A, B, C -- A, B, C -- A, B, C -- ...
The dashes indicate an initiatve round boundary, which has almost no effects on game play.
Now when someone refocuses, they lose all their actions this initiative round. They can't even move. They will go again in the next initiative round as if they'd rolled a 20.
So, if A refocuses, the sequence changes to:
B, C -- A, B, C -- A, B, C
Meaning A has given up an entire action to no purpose whatsoever.
If B refocuses, the sequence becomes:
A, C -- B, A, C -- B, A, C
Meaning B has essentially bumped himself down in order to go after C, to no purpose whatsoever, since this sequence is the same as (A, C, B -- A, C, B -- )...
If C refocuses, the sequence is now:
A, B -- C, A, B -- C, A, B --
Which means C has not really lost anything, but has accomplished nothing besides raising his initative, which I think only matters for the sole case of the DMG rules for entering into the middle of combat.
If you are using those rules, and you are going near the end of the initiative sequence, and a Refocus would put you at or near the beginning -- then you might consider doing a Refocus, in a "why not" kind of way.