To make my decision regarding supporting an initiative I don't look at what's in it. Instead I always look at who is endorsing it. With Prop 10 you have support coming from various SEIU unions and Democratic Socialists of America groups. That right there tells me this will be bad for our state and gets a big no vote from me.
It's no skin off my nose since I live a thousand miles away with no desire to get any closer to the on-going trainwreck there, but I can see why both some property-owners and some Leftist leeches would support it.
Property owners might see it as something their own locality isn't likely to do (Not in places like SF of course) and see it as removing a State-held sword from the space over their heads.
The leeches like SEIU see it as probable that they will be able to gain enough political power to pass more-sweeping rent control in many more places than now, and perhaps get so much control in the State legislature that they can pass State-wide rent control that'll affect every city.
In the long term I'd say the leech version is the more-likely outcome by far.