If you live in a climate where there is a hard frost in the fall, you can discontinue it during the winter if preventing fleas is your main concern. Jack will also get his last dose the beginning of Nov. and then no more until probably April. We don't have ticks here in my area, so I'm not sure about that, as I don't know the life cycle of ticks.
I also use Frontline year round now. I've just started finding the smallest ticks on both dogs in the last few days after they've been in the yard. The edges of the yard are not all cultivated or mowed but I do have deer fencing. The deer are all around outside the fence though. Given the crazy weather, & the fact that I found ticks on Luca through December last year, I figure better safe than sorry.
If I lived in a climate where the fleas and ticks could live year round, I would continue the Frontline all year. It's just not worth it to take the chance, believe me.
We have a hard frost a few nights a year where we live (in Southern California but at 1,500 feet elevation) and don't have flees on our property.
We do use Frontline during the Spring, Summer and early Fall months to prevent our dogs from picking up random fleas from other areas but, not on a monthly basis.
We are traveling in our motorhome to Texas, Mississippi and Louisiana over the Christmas Holidays and beyond - so we will continue using Frontline during the period of our trip.