For gamers they just don't. And Matlab, SPSS don't care about this lag. Instead of taking 5 seconds it may take 10. Is that so bad?

The MacBook Air models may not have huge drives so you must plan ahead. No one but you can guess this but 128 or 256GB drives are too small for compsci folk.

Apple refurb gets same warranty as new. And you get Apple care for the number of years you need it covered.