We wnt to match the moisture content of the lumber during storage after drying, match the moisture content of the wood during manufacturing, and match the MC of the product when ti leaves our shop with he MC it will achieve in use. The reason is that moisture changes are accompanied by shrinker (loss of moisture) or swelling (gain of moisture). Sometimes the size change, due to grain angle or other factors, causes warp as well.
For furniture, cabinets, flooring and other wood products used inside a home or office, the moisture in wood when the heat is on will run about 6% MC (30% RH). During the summertime, the moisture will run around 9% MC. Of course, Denver is drier and Florida and coastal areas are wetter. But for most of the USA, 6% to 9% is the common range, winter to summer. Because we know that drying is often more of an issue that swelling, we target a little bit drier, so that is why we see 6 to 8% MC. Based on 50 years of experience, I suggest that a target of 6.8% MC is ideal for inside most homes and offices in North America and the variation around this value is + or - 1% MC.
Softwoods shirnk and swell less than hardwoods generally. Softwoods are often used within he walls, or in other locations that are more humid than inside the hours. Softwoods machine more poorly when under about 10% MC. Therefore, 10 to 12 % MC is more reasonable for softwoods.
As mentioned, a moisture meter should cost over $200. Cheaper meters are almost always not as accurate. Foreign made meters are notorious for having poor calibrations for North American woods. Fast repairs and maintenance are often impossible as well.