In the 1980's my parents were paying $20 per month for a loan for a 4 bedroom period home in Canterbury. Inflation can be very kind to loans.
When I first began investing interest only loans were the hardest concept for me to grasp.
Why not pay P&I when it doesn't seem that much more than IO and actually pay the debt off? It made no sense at all to me.
Now my thoughts are:
If you have extra money and you have PPOR debt and you want tp pay down debt then put any extra money off that debt not your ips.
If you borrow say 1 mil on interest only at 7.56% it would cost you $6,300 per month and on P&I $7,034. So in this example there is a difference of around $700 per month which might might the differnce between being able to comfortably afford to hold onto thia property or not or being able to invest in further properties or shares. $700 is a lot to tie up each month.
If you don't have a PPOR and have entra funds then it allows you far greater flexability if instead of paying the money off the loan directly you place it in a 100% offset account. This has the same effect on the interest as paying off the loan directly. You are able to redraw it at any time for any purpose. To maxmise this effect you could place your whole salary in this account and reduce your interest payments further.
The main game with holding growth assets is to hold as many as you can because 10% growth on say 100K is $10K and on 1mil is $100K. So that extra $700 per month might allow you borrow another $100K and therefore $10K more growth per year.
Of course all of the above is personal choice and each of us has to sleep at night. Me personally, I have trouble sleeping at night f I have unspent equity.