One dynamic that’s in play is the concept of making your record.
When a litigant appeals an adverse verdict, he must typically identify an error–during trial, says the appeal, the court committed such-and-so error, which undermined my right to a fair trial. If this error had never happened, I never would have been convicted.
But that opens up the possibility of gaming the system: when an error happens, remain quiet. If you’re acquitted, then you’re fine; if you’re convicted, complain on appeal about the heinous error that cost you your freedom.
To combat this play, the general rule is that you cannot complain on appeal about a trial error unless you objected to the error at trial, with enough specificity that the trial judge has an opportunity to intelligently rule on your complaint, correct the error and limit any prejudice you might suffer. This is why you must generally offer the grounds for an objection.
So under that rule, “gaming the system,” becomes objecting on a wide range of grounds that are even slightly defensible. At least you made your record, and if you need to appeal on the point, no one can say that your appeal is barred by Rule 5A:18, so suck it.