Most investors know all about the tax reasons for "harvesting" capital losses. But if you're considering a sale of assets that have gained in value, keep in mind that harvesting long-term capital gains can offer tax advantages as well.

Capital gains and losses from securities transactions, as well as other dispositions of capital assets, are used to offset each other. Thus, if you're showing a net capital gain for the year, you might realize a loss, especially at the end of the year. The loss can negate the gain plus up to $3,000 of highly taxed ordinary income. And any leftover losses can be carried over to use the following year.

On the other side of the ledger, short-term capital gains from sales of securities you've held for a year or less are taxed at ordinary income rates. But gains that qualify as long-term—from selling securities you've held longer than one year—are taxed under special rules.