Don’t Make Me Think, Revisited a common Sense Approach to Web Usability Steve Krug

Breeding chameleons
The siren song of one-design-fits-all-screen-sizes has a long history of bright
hopes, broken promises, and weary designers and developers.

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If there are two things I can tell you about scalable design (a/k/a dynamic
layout, fluid design, adaptive design, and responsive design), they’re these:
It tends to be a lot of work.
It’s very hard to do it well.
In the past, scalable design—creating one version of a site that would look
good on many different size screens—was optional. It 
seemed
like a good
idea, but very few people actually cared about it. Now that small screens are
taking over, everybody cares: If you have a Web site, you have to make it
usable on any size screen.
Developers learned long ago that trying to create separate versions of
anything—keeping two sets of books, so to speak—is a surefire path to
madness. It doubles the effort (at least) and guarantees that either things
won’t be updated as frequently or the versions will be out of sync.
It’s still getting sorted out. This time, the problem has real revenue
implications, so there will be technical solutions, but it will take time.
In the meantime, here are three suggestions:
Allow zooming.
If you don’t have the resources to “mobilize” your
site at all and you’re not using responsive design, you should at least
make sure that your site doesn’t 
resist
efforts to view it on a mobile
device. There are few things more annoying than opening up a site on
your phone and discovering that you can’t zoom in on the tiny text at
all. (Well, all right. Actually there are a lot of things more annoying.
But it’s pretty annoying.)
Don’t leave me standing at the front door.
Another real nuisance:
You tap on a link in an email or a social media site and instead of
taking you to the article in question it takes you to the mobile Home
page, leaving you to hunt for the thing yourself.

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 Always provide a link to the “full” Web site. No matter how fabulous
and complete your mobile site is, you do need to give users the option
of viewing the non-mobile version, especially if it has features and
information that aren’t available in your mobile version. (The current
convention is to put a Mobile Site/Full Site toggle at the bottom of
every page.)
There are many situations where people will be willing to zoom in and
out through the small viewport of a mobile device in return for access
on the go to features they’ve become accustomed to using or need at
that moment. Also, some people will prefer to see the desktop pages
when using 7″ tablets with high-resolution screens in landscape mode.