With achieved grades below the standard requirements, at "top unis" (per your description) unless you are resitting you will not get an offer normally. Students predicted under the standard requirements by one grade are often recommended to apply (with a few exceptions) as unis realise predicted grades may not represent final achievement and making the a conditional offer of the standard to a student predicted under the standard offer is very low risk as if they don't achieve that conditional offer (i.e. achieve their predicted grades or lower) the student won't be accepted unless the uni decides to take them as a near miss applicant - the uni have no obligation to take that student.
For applicants with achieved grades who are not resitting, they are not made conditional offers. They either receive an unconditional offer or an immediate rejection. Thus without resitting, you only have two possibilities and most "top unis" aren't going to take a weaker student with achieved grades when they could make conditional offers to students with stronger predicted grades (or even the same predicted grades, at no risk to themselves).
So there is literally no point unless you are resitting. You don't have a lower chance, you have functionally zero chance unless their standard offer is significantly inflated from the standard of students they expect to be accepting on results day anyway (which one or two unis are known to do...while claiming to be "top" unis).
But as above there is basically no risk to yourself. But don't expect anything other than a rejection in most cases, I would say.