I've done it in the past, especially after the Priceless Surprises promo IHG had by sending in postcards some years ago.. yes, I didn't get full value out of the IHG points, but I was also just looking for ways to boost my Avios balance, and IHG was secondary. I had (still have) the IHG Chase Visa that gives a 10% rebate on redemptions, so I got a nice IHG points rebate too (which I probably converted to Avios later on). All done by phone at the time.
Haven't converted in a while but I do track my IHG points on a spreadsheet as potential Avios in case my balance ever needs topping up. I usually wait for a 25% conversion bonus, but I don't think BA have offered any of those since the pandemic.