10ft Square vs 5 ft burst

What is really the difference between a 10 ft sqare as in the Grease spell.

Or a 5 ft burst ?

The effects of Widen Meta-Magic comes to mind as being a difference.

A bit late on the reply sorry, a burst is unique in that it does not effect targets that have total cover. A burst is also usually considered a sphere.

"A burst spell affects whatever it catches in its area, including creatures that you can’t see. It can’t affect creatures with total cover from its point of origin (in other words, its effects don’t extend around corners). The default shape for a burst effect is a sphere, but some burst spells are specifically described as cone-shaped. A burst’s area defines how far from the point of origin the spell’s effect extends."