Yes, it does.
If your images are too big it will slow your website down.
If they are too small, they will appear grainy or blurry.
When we talk about size in regards to images we are talking about pixels.
Pixels are tiny, tiny dots that when grouped together make up an image.
The physical size of your image might be 6 cm x 6 cm, for example, but the pixels can alter a lot.
The more pixels the denser your image is and the better quality.
You’ll see low pixel images are blurry and grainy.
Some websites and formats allow you to adjust the size of your pixels.
If you have a very high resolution image (loads of pixels) then you can shrink it down without losing any of the quality.
However, enlarging a low resolution image can’t be done very successfully.
It’s always a good idea to buy or create medium sized images.
These should be around 500 pixels high x at least 750 pixels wide for a rectangle image.
For square 500 x 500 is great; and vertical, 350 x 500.
That way you can be sure that your images are both user friendly and look great on your site.