The reason to hold bonds in tax-deferred accounts is because bonds generate ordinary income which is taxed at ordinary rates, just like tax-deferred account withdrawals. Qualified dividends on equities and long-term capital gains are taxed at preferential tax rates, generally 0% for those in the 15% tax bracket and lower and 15% for those in the 25% tax bracket and higher.
Holding equities in tax-deferred accounts essentially converts income that would be taxed at 0% or 15% to income that is taxed at 15% or 25%... and that 10-15% difference adds up. Also, while a portion of international equity holdings are not tax preferenced as described above, you get the foreign tax credit if you hold international equities in a taxable account and you lose that benefit if you hold international equities in a tax-deferred account.
Also see
https://www.bogleheads.org/wiki/Tax-efficient_fund_placement
Liquidity is not an issue, you just sell taxable account investments as needed to fund spending and then sell bonds and buy stocks as needed in your tax-deferred accounts to rebalance.