The thing with panniers is that if I suddenly decide to go somewhere on the way home from work, like tonight, had an idea for tea and fancied a beer, though not drinking alcohol due to excesses of the b/hol weekend, so it wasn't an issue to go to tesco for some packs (on a BOGO½P) of alcohol-free lager, instead of pratting about going home and back out again
Plus, despite being the only one cycling at work, with plenty of people with cars, guess who is the only one who can be bothered to be responsible for the tea and biscuit provisions whilst the normal tea-club person is on holiday, so both panniers had to be pressed into service for Monday's milk run.
Would have needed my backpacking rucksack for today's little lot (no lockers so have to carry change of clothes, lock and everything back and forth) and wouldn't have fancied that.
There is always the option of a racktop bag - less bulky but still sweat-free - for which I have a seatpost mounted rack for the road bike and the MTB, since I must admit, the rack wasn't "right" on the Virtuoso. Can't carry as much as panniers but a good alternative if you can't face fitting your bike with a full rack and panniers