It's kind of a debatable question and can come down to you chin, your experience as an owner, and your vet. Personally I don't think yearly checkups are needed, and can stress the chin out weakening it's immune system making it more likely to getting sick from something at the vet. On the other hand a yearly checkup can sometimes help discover an illness or issue earlier then you might have noticed. I guess it depends on how well you know your chin and how well you know what to look for to notice an issue. I know in a lot of areas still vets don't know chins very well and may over look something or dismiss it as normal because it's normal in another small animal. If your chin doesn't get stressed out going to the vet though, it may be worth taking it in for checkups to also give your vet more hands on experience of what a normal healthy chin is like, instead of just seeing them when they are sick or injured.