If I had been smart enough to buy Google, Facebook, or Amazon a few years ago I would be taking some or maybe all profits there. If Apple goes below 100 I will start buying again and possibly selling covered calls on it.
My IRA's have a really long time horizon so although I'm still putting cash in them every month I'm not buying anything. I'm not selling anything in there either because I just buy SPY (S&P ETF) and occasionally some down and out sector ETFs every month.
Nobody would advocate actually withdrawing from an investment account. Just move it to safer investment options.
Even if you passively invest in a mutual fund, the funds internal transactions show up as capital gains that get reported to the IRS, and you have to pay the tax.