A simple case if you just need more memory. In addition, by moving to a higher class of instances, you βrentβ more processor cycles, so your requests can be executed until they are finished before downtime again. It really depends on the application, if it makes sense to switch. This Google Developers Video has a section where this is discussed in more detail:
https://www.youtube.com/watch?feature=player_detailpage&v=T_BQevqRp44#t=2094s
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