There can be no strategic reason for not making the proper objections and preserving the record if the goal is to provide “effective assistance” as intended under the Sixth Amendment. Thus, there can be no strategic reason for not filing a motion for new trial when the client was convicted at trial.
a direct criminal appeal is completely useless without the trial attorney making doubly sure that any appellate issues were properly preserved for the appeal or beyond. In this sense, what you don’t know can hurt you, badly. And you must have lost and been convicted (otherwise, an appeal has no purpose).