There is almost never a good reason to throw out another adult person's possessions without their permission

Yes, if I think "what is a reasonable reason to throw out someone else's stuff without asking them for permission beforehand?" I come up with off the top of my head

a) the stuff is actively hazardous in some way - mould, asbestos, food poisoning bacteria, radioactive, smallpox

b) you're flushing drugs before a police raid to avoid the person whose drugs they are getting arrested

c) you're disposing of incriminating political leaflets/books before an imminent police raid if you live in a country where "women should have the right to vote/not wear a hijab" can get you arrested or jailed

d) as c, but for abortion access/abortion rights before an imminent police raid

e) you don't live with them anymore, and you've said "please collect your stuff within 30 days/60 days/90 days or I will throw it away" and despite repeated reminders, they have not collected their stuff and they don't have a reason (like eg being in hospital) for not collecting their stuff