Should you end your client's website development before putting it online ?
Short response : No
No because usually you need to most early you post something on the internet the most traffic you can get, and a good way to get traffic is by creating meaningful content like @Gary Vaynerchuk always say.
It can be by writing articles on a blog, responding questions on a forum, so if you are planning to finish a website in 1, 2 or 3 months or even more i will suggest you to start by doing the blog module (if there is one) online under the real domain name of the website and allow your client to publish content there. After the blog you should open the forum and even the event module if there is one. The goals there is to grab some traffic and some recognition over the internet and within your client's communities (Facebook, Instagram, Pinterest, etc) by the way you will allow your client to get quickly get some feedback about his product (at least the one he is planning to promote on his website). What are some of the advantages of a such approach ?
- Start to see the value before launching the whole website
- Allow your client to get feedback about the need of his market without having to wait a long time
- Being truly agile, not only with words but with actions
- Save money on SEO campaigns