Roughly, it varies by stage, and how big the firm is.
Most Big VC Firms ($600-$1b+ in a fund) want to own 20%+ of a start-up, ideally even 30%. They may be OK with 15%, but below that, they’ll probably pass on most deals.
Most Micro-VC Funds ($50m or smaller fund) would like to own 10% or more, but typically model around 7% average ownership.
Then many funds will have exceptions for smaller investments for a variety of reasons, from getting their more junior investors experience, to supporting founders they’ve invested in before, to doing seed investments to “learn”, etc. But these exceptions to ownership targets make these investments non-core. Typically, the funds are not as committed / investing in these deals.
Once you get into late-stage deals, it’s more about absolute $$$ invested than % ownership, but in Seed, A, and B deals, ownership % is important.
The bigger the fund, the more they want and need to own.