I have not really been able to maintain any kind of regimen, so I've had a chance to see how I do in the various scenarios of time on/time off/different type/etc... I really do think it depends on many things.
If I owned a plane and relied on it for travel, particularly if I had the IR, I'd try harder to fly regularly, and cover what's appropriate on those flights. And of course if you are paid to fly in any capacity, you have to stay "in training" as it were. But in my situation, I can be a little less hardcore about it, and still remain safe.... if I take the variables into account.
The key, I think, is common sense. If you've been doing nothing but pattern work and milk runs on fine days to familiar fields, even if you've been doing that every day for the last year, you may not quite be ready for a long X-C, with the chances of changing weather, waning daylight, or nibbling at fuel reserves. Then there's fatigue, get-there-itis, etc.
On the other hand, if you've only been dashing off from A to B, you might not be ready for a situation that requires MCA flight or a spot landing. Then there's the pilots who are always "in the system" and are uncomfortable operating at an uncontrolled field, and vice-versa.
The specifics of a given flight can make a huge difference.
I haven't soloed anything in over a year, haven't even soloed the glider yet, but I know I could take a familiar powered type around the patch a few times in fair winds without any trouble. I'd probably even make some good landings. In not-so-fair winds, I'd probably still do OK, but it would not be pretty. Having all the glider time and quite a few turns at the controls in others' planes would make a difference, but it's hard to say how much.
The one dual flight I made during my long hiatus went fine, after almost 2 years of no flying at all- the instructor didn't need to intervene, and I felt quite comfortable. And when I dove back in for a FR over a year after that, again, my basic skills were not so bad... but the other stuff had atrophied for sure. Planning, rules and regs, weather, emergencies... all the same stuff more active pilots tend to slack off on.
So I certainly wouldn't set off on a long trip or tackle adverse winds without working up to it, and without thinking and studying some beforehand.
And the next time I do fly alone in a powered aircraft, I will be practicing. That's my usual M.O. after a hiatus: MCA, stalls, maybe a power-off approach. Reciting emergency checklists, and seeing what the hands remember. And I like to leave time for more landings than is "necessary".
It's wise to do an exercise or two, or at least do something differently than usual, even on that short breakfast fly-in flight... quality of time definitely counts more than quantity, I don't care how many total hours you have, or how often you fly. Thinking of yourself as a student, always ready to learn something, is much more useful.