If I'm unemployed and I have bills to pay, a paid probation period is the better option - even if I get fired after 90 days, that's still 3 months' salary. On the other hand, if I already have a job, joining another company is a big risk - I'm giving up a comfortable position for a job I might lose in 90 days if it doesn't work out - maybe I'll be in over my head, maybe I don't get along with the manager or the team, whatever. A long interview process gives me plenty of opportunity to gauge my prospective employers and back out at any point.