If it needs it, you will hear an annoying clicking noise coming from under the valve cover- especially with it idling with the hood open. The clicking will speed up with engine rpm.

Be sure to maintain at least the minimum clearance. Going too tight can lead to burned valves.

The tool TomO showed makes life much easier. search "honda valve tool" on Amazon, you can get them pretty cheap. It makes it much easier to toque down the lock nut without changing the clearance.

Check your owners manual for scheduled maintenance or call the local dealership. It should tell you. I've seen recommendations that vary anywhere from every 3000 miles, to 15000 miles to 50000 miles to never (for hydraulic lifter cars).

I had a Mazda pick-up with a 2.0L and recommended valve adjustments were every 30,000 miles. I always adjusted to the mid range of the clearance because I have seen valves tighten up during operation. It happened to my dad a couple years ago and he had to have a complete valve job. Cost him about $600. if I remember right. If you go to the mid range you will have a few 1/1000's either way.

Its been awhile since people had to worry valve about clearances getting tighter over time- but that would be damaging to the valves (burning/warping).

That must mean that the valve seat is being pounded thinner- which was a concern with using unleaded gas in old engines designed for leaded gas.

Adjust them once a year. It can help you pass smog and give you a smoother idle.

Kinda depends on the design of the engine really. This is a problem with my old (1985) mercedes. Couple it with timing chain wear and you have a recipe for disaster...

Old VW's and Porsche's used to do this as well for the first few thousand miles after a rebuild. The reason is that as the engine "settled in" and all the mating surfaces seated and gaskets compress the overall deck height will change. You won't find that in anything but pushrod engines though.

Valves can also stretch depending on how hard the material or how strong the springs are, but that's probably not an issue in engines under about 15 years old.

For a honda though, I'd say you're safe adjusting them to the minimum clearance.

My old 911 is due for the adjust. What a pain it is with 4 valve covers,,half (intakes)in the engine compartment above and the exhaust valves on your back below. Spendy gaskets too!
The 911 6cyl engine normally expands in width 1/8" from cold to fully warmed up.