thats true. even if not amazon scale.. lets say you building multi tenant SaaS product. cell-architecture provide strong tenant isolation avoid noisy neighbor problem. other benefits like deploy changes to one cell so tenant may request delaying upgrade if they need to do pre-req work before hand.

for ordinary service use case or web site.. most probability do not need this. over engineering infrastructure when should focus on customer and problem domain..thing that increase top or bottom line.

source: principal SDE who launched several services at amazon using cell architecture.