No long-term problems are caused by not antifouling, but you may of course get a lot more fouling next year.
Some people antifoul religiously every year, others leave it until the old seems to have stopped working. Its more essential for a racing than a cruising yacht. Areas/marinas differ a lot regarding the amount of fouling you pick up, and a rolling stone gathers no moss (well, less than it would otherwise).
some antifouling manufacturers say that theirs will do two seasons. Its up to you - you may find that when you are off for your august hols - your boat is covered with weed and you have to slip at vast cost - in which case you will have wished you had put a new coat on.
Personally, I always reantifoul as to slip a 40 footer mid season will cost more than the antifoul (£160.00), apart from the hasle
Agree entirely - if the boat is out of the water now - you may as well get it done. I antifoul and do the boot top each season and don't get barnacle growth at all - so I feel I may as well stick to current practice and keep doing it each Easter just before she goes back in.
I used to, but now only antifoul once every two or three years. Main problem locally is with slime. As that grows mainly within a few inches of the waterline, it can be cleared in the water, going around the yacht with a scrubbing brush occasionally. Interestingly, the grey mullet in our marina make a pretty good job of cleaning the boats of slime - but they won't touch freshly antifouled boats.
I antifoul when I need to a look under the boat tells me when, i also find it cheaper to do it after the spring rush, when most yards are empty, the days are longer and weather is better aswell. I can get mine done in two days, two people getting after it, no pussy footing about, even if its raining you can scrape.