This is just a different way of saying what's already been said, not really anything new about it.
If you've 'tuned' an antenna, made it resonant and done the impedance matching, then it shouldn't need anything done to it until something changes. The first thing that comes to mind is what kind of antenna are we talking about, mobile or 'fixed'? Things can change with either, so both are subject to wondering about occasionally. Checking every once in a while is typical/normal. How often should that be? Beats me, when ever something changes or when you feel like it?
'Fixed antennas'
(I'm sort of uncomfortable whicvh that 'fixed' phrase, but whatever.) Non-moving/movable antennas tend to change less than mobile ones. That's typically because they don't move around a lot, aren't subject to the same amounts or kinds of vibrations, stresses, etc, but they do change. That's usually connected with corrosion, connections/joints, and things changing around them (growing, being chopped down, whatever). Think about that, I'm sure you can come up with as many of those thingys as I can. The simple side of that is that nothing ever stays exactly the same, and since part of that tuning is making an antenna 'comfortable' in it's environment, and since that environment is always changing... and I'm sure you can see where that's going, right? I don't know about where you live, but around my house them stinking @#$ squirrels don't seem to like antennas or the things that hold them up. So, a fairly regular check, or at least paying attention to the radio is sort of necessary. (12 ga. thingys work very well with this sort of changes. The neighbors don't like it but so what.)
Mobile antennas.
Same basic ideas, just more of them, sort of. The 'hard' mounted mobile antennas tend to not change as much as the movable kind, simply because they don't get moved as often. If a movable antenna gets moved, it doesn't hurt to check it to make sure it wasn't moved 'too much'. Since mobile antennas are subjected to more vibrations than the 'fixed' kind, it pays to pay attention to anything that can come loose on them. I don't think making a 'fetish' of tightening things is a real good idea, but doing so every so often probably wouldn't hurt. Driving under 40 miles of low hanging tree limbs sounds like a good time to re-check that antenna, you know? (Do that at the right speed and it sounds like a metalica beat-box, don't it??) Adding something metal near a mobile antenna, or doing a chop-n-channel on the roof line is another good time for antenna checking. An occasional check after really different weather conditions probably wouldn't hurt either, once anyway maybe.
So carrying around a few meters isn't something that's absolutely necessary all the time. Unless you just happen to have a few extra meters that you want to leave hooked up all the time. Or maybe have on in a radio? Then it's just a matter of paying attention to 'whaz-hap-nen wid-da ra-did-di-o', sort of. There are two kinds of "can't check, what the heck" sort of people. Those that it really bothers, and those that is doesn't. Both kinds have their 'pluses'. You decide which you are.
And then there are those antennas that are only going to be put up for fairly short period and then taken down for use at another time. With those, take your meters.
- 'Doc
Some exaggeration in the above, probably not too much... sort of.
(all puns intended)