Well, as you wrote it I wouldn't call it a strategy since you are exchanging one fund for a very similar fund. Both are just fine in a taxable account.
However, if you had written, "I would like to tax-loss harvest my VFWAX and replace it with VTIAX, is that a good idea?" The answer is: It's a great strategy.
I would not do the exchange until VFWAX and VTIAX had stopped losing money in order to get the maximum tax-loss harvesting benefit. There is absolutely no rush on this at all. Maybe wait until a day when VFWAX or VTIAX have dropped 2% or more (watch VEU and VXUS for intraday pricing) and submit order before 4 pm.
Nonetheless, one should not let losses in a taxable account become long-term losses. One should TLH before they go long-term. So if any part of the VFWAX has a short-term loss position, sell it before it goes long-term.