I hate-hate-HATE tossing excess insulin! It's not the expense, it's the waste.
But then ... there were those 2 months (in a row) where I tried to "conserve" by staying on the old bottle o' basal. Each attempt led to 1 miserable day at the workplace. I spiked sky-high on everything and nothing, had to sneak away constantly to test and shoot up with rapid (which was fresher, thank the Force). Counted the minutes 'til I could get to the sweet new bottle waiting in the fridge at home.
Not fun, given a 9-hour day plus 45-minute commute.