There's been a lot written about the merits of buy-and-hold investing. Unfortunately, many investors are confused by the term and instead employ a buy-and-set-it-aside strategy. This can be a grave and costly error, as holdings can swing widely over time and tweaks are often necessary to bring a portfolio back in line with an investor's stated goals.
Maintaining a healthy portfolio is a lot like keeping your car or a household appliance in proper working order. You need to occasionally tinker with the parts in order to keep your portfolio running smoothly and efficiently.