The only time when interviewing someone I ask about personal hobbies etc is when the decision was already made. At that point it was simply to get a better sense of the person I will be working with.
When I've been interviewed it was telling when the person didn't realize I was interviewing them also.
I just went through a slew of interviews where I got several questions early in the on-site technical interview about my hobbies. Actually had an interview a couple months ago where there was a dedicated part for a "cultural fit" interview. I think if I knew I was going to get hired it would likely be less of an issue for me, but I still think you should consider kind of what these kind of questions communicate in an interview context and how interviewees will be primed to answer them. "At will employment" generally means employers can choose to fire you or not hire you for an enormous number of petty reasons, and that knowledge is always shaping how I perform in an interview, and generally leads me to be pretty tight-lipped about anything about myself. I had an interview recently where an employee that was part of the hiring process was able to find out that I have left wing politics based on a github organization I was a part of. I didn't get that job and, like many companies, they weren't willing to provide their rationale, so I'll never know if that was an important factor.
By the point we start that aspect we have generally stated an offer will be made. You can generally tell if the person will be a culture fit during the real interview, if a person can't from just normal human conversation that person shouldn't be interviewing others.
The hobby etc questions were basically just shooting the shit getting to know a potential new member of the team if they accepted.
In essence, will the existing team like working together with that person, ignoring all the purely professional aspects. Personality, communication, agreeability, compatibility (or conflict-avoidance) regarding various non-work opinions, alignment regarding subjective styles of work (e.g. 'move fast and break things' vs 'verify everything 3 times, even if it causes a delay' - you need to fit the organization's "style"), etc.
Frankly an organization's "style" is a bunch of unexamined, calcified social biases that companies screen in interviews for because they don't like to be challenged on them. Or in the more malevolent cases its outright bigotry that's given cover as something else. Heterogeneity of methodology is actually good (especially at startups, which often operate in ways purely driven by the whims of inexperienced founders), and the people you interview can often teach you a lot. "Culture" is a joke, there's nothing cultural about these things.
Microsoft in the 90s used to hire on talent and wall off anyone who "didn't get along". They could code in peace and their manager handled outside communication.
When I've been interviewed it was telling when the person didn't realize I was interviewing them also.