While this question has been asked in a variety of contexts before, I can't find any information pertaining specifically to sites targeting very large audiences - for example on the scale of hundreds of thousands or even millions of users.
When writing sites that target smaller audiences (such as intranet hosted data driven sites that handle from a few to a few thousand users) we only tend to follow best practices within the confines of our project budgets/deadlines - i.e. developer costs, rollout schedules and maintainability have a far bigger impact than we would often like on how we code things.
Some things are also negligible (to a point), for instance delivery time, image compression/size, bandwidth because the nature of a LAN hosted application tends to mean that there is a relatively small amount of financial cost that (within reason) we don't need to worry about too much.
However, when looking to target a much broader audience for instance an audience of (hopefully) millions of users:
- Are there any best practices that no longer need to be worried about (i.e. become more negligible the larger the audience)?
- Are there any practices that should be adhered to even more tightly?
- Also, are there any practices that only really come into play as your audience achieves some critical mass [and what would that critical mass be]? i.e. applying artificial constraints that wouldn't begin to concern you on a private network
Examples I've come across so far are:
- Host codebases such as jQuery on Google as it's delivered from Google's CDN and can be served much faster than from your own servers. This will also help keep bandwidth costs down for delivery of your site.
- Host images on a CDN for the same reason as hosting your javascript code elsewhere.