For individual stocks, churn can add up as trading fees eat into your profits. Obviously, this happens more with small portfolios and frequent trades. Even if you have no trading fees, if you buy/sell every year and pay capital gains tax on your earnings, then that taxed portion goes away forever and will not create any more returns, whereas leaving it invested allows it to compound until you finally do pay taxes. Over 10 years, this would create an annualized difference of about 0.2%/year.
"Church"? Church will reduce your gains, to the tune of 10% per year.