The problem with leasing is if you grow too fast you're stuck, and if you have to make cutbacks you're also stuck with the lease.

This is the real advantage of them. Even if it costs x% more the value of not being stuck with a lease for a long time is definitely worth it. A lot of financial firms in London are moving to them, leases are typically long (10 years with a 5 year break), and with the uncertainty around brexit it makes total sense to transfer the risk to WeWork et al for not much money at all.