Performance as experience.
WHY IT IS A DESIGN CONCERN
Speed is experienced before anything else about the design.
WHAT PEOPLE DO WHEN SOMETHING IS SLOW
Leave.
WHAT AFFECTS PERCEIVED SPEED
How quickly something appears Whether progress is visible Whether they can begin before everything loads
WHAT TO DO
Show the structure immediately Load content progressively Prioritise what is visible first
WHAT DESIGN DECISIONS COST SPEED
Large images Many fonts and weights Heavy scripts Video that loads automatically Elaborate effects
WHAT MATTERS MOST HERE
Data cost, not only time.
Visitors on metered connections pay for every element.
WHAT TO DO ABOUT IMAGES
Size them for the display Compress them Use appropriate formats Load what is off-screen only when needed
WHAT TO AVOID
Layout that shifts as content loads
WHY
It causes people to click the wrong thing.
WHAT TO TEST
On a phone, on mobile data.
