Product planning is just a waste of time.

After attributing failure to spending three months on mockups and market research before doing any actual development, the author concludes with:

After the past experiences I don’t plan anything. I don’t even do market research... We just jump in and start developing, after doing some sorta brainstorming(what features we should add, etc). We ask a couple of target users what they think and decide whether we’re gonna add that feature or not.

No, you ARE still making plans, they just happen to be ones that are better and more appropriate.

I see it as a trade-off - you do need a lot of flexibility to adapt to unexpected things and disappointments and successes, but at the same time, you need to make good decisions fast. Planning is basically speculative decision-making, and that's valuable.

The kind of planning that I think works better is a web-style plan - less focused plans that cover more contingencies and are applicable in different circumstances. Have a general idea of what to do as a response to major stimuli, and have some ideas of things which build well upon each other. "Well, if we have a lot of users, we can leverage that to do X" is a plan that works somewhat independently of how you got those users, for instance. "If we wind up needing to boost traffic at some point, our ace-in-hole can be Y", or "If Z happens, we can capitalize on that by doing Q".