There are brokerage firms offering free trades (for example Zecco with a $25 K balance). At such firms the cost of trading is the bid-ask spread (and the value of one's time). I think for some bond ETFs that trade with fairly tight spreads, the cost of trading is less than 1% annually, so that the tax savings could exceed the trading cost for investors who have capital losses carried over from previous years that can be used to offset the capital gains. Below is an example using JNK, the junk bond iShare (ETF).
I wish there junk bond funds that paid distributions annually or quarterly, which would make it easier to avoid taxes on income distributions.
symbol JNK bid 31.070 ask 31.090 mid 31.080 % spread 0.0644 #trades/year 12 % trading cost/year 0.77 % dividend yield 14.00 tax rate (state+federal) 40% % dividend tax 5.60 ratio of tax to trading cost 7.25