Maybe you won't.

IIRC local machines by default only caches stuff for a very short time which makes sense for personal computers.

On company networks however I'd expect sysadmins to run nodes to reduce upstream bandwidth usage.

Edit: see also https://news.ycombinator.com/item?id=10329262 the specific example is the exact opposite but I see no technical reason why you cannot do this the other way around.

There will be incentives in the future, both in terms of promoting a good seeding/leeching ratio like bittorrent ("bitswap"), as well as http://filecoin.io/

And how would you deal with materials that could get you either dead or imprisioned? Can you elect not to host content? For example, in china, you have a situation where you can be materially affected by political content. https://www.privateinternetaccess.com/blog/2015/10/in-china-... Or what if you happen to live in a country hostile to LGBT content, like russia or Zimbabwe, where it may be dangerous to host such content?

That is exactly what ipfs does, in contrast to e.g. freenet. Mirroring is opt-in.

Because you might like that company/organization/website. As the IPFS dev said in other replys in this thread, you can choose which sites you want to help