If your title and description look genuine then as far as I know, Google will treat them just the same as it treats shorter titles and descriptions. On the other hand, if they look like they're stuffed with keywords to bait search bots, Google will treat them with the contempt they deserve (that is the same however long they are!).
The reason that those limits have come about is because that's all that Google will display in its results page. If your title or description are longer than that, they will be cut off and so searchers won't see the full text. You might be OK with that, and there might be good reasons why you want a longer title or description, but most of the time it's better to try to keep it within the limits so that searchers see the text in full.