I don't think this is bad advice, but I think it's fairly situation-dependent. Other comments have already called out issues when working on a time & materials basis, etc. I work for a mid-sized consultancy; we do not charge anything up front, but we don't have the cash flow concerns alluded to in the article.
As long as you understand the message you are sending to the client ("I'm concerned about cash flow"), and are OK with that, it's a fine approach. Presumably most free-lancers are OK with the idea that they are not projecting a "big company" image.
Another thing to keep in mind (particularly at the end of the client's fiscal year or fiscal month) is that they may want you to invoice early so they can avoid an accrual. This probably applies more to large businesses than small clients, but you may be able to negotiate for faster payment (e.g., net 10) in return for invoicing to their fiscal schedule.
As long as you understand the message you are sending to the client ("I'm concerned about cash flow"), and are OK with that, it's a fine approach. Presumably most free-lancers are OK with the idea that they are not projecting a "big company" image.
Another thing to keep in mind (particularly at the end of the client's fiscal year or fiscal month) is that they may want you to invoice early so they can avoid an accrual. This probably applies more to large businesses than small clients, but you may be able to negotiate for faster payment (e.g., net 10) in return for invoicing to their fiscal schedule.