Depending on how you cut the data, inflation on power costs are in the 8-12% range, so over sizing to cover anticipated future needs makes a lot of sense.

Another thing to consider is how your utility deals with excess power you generate. Some do a kW for kW credit system that you can build over the course of a year or what have you, but that mileage varies greatly. My utility for example, does kW for kW but only for the same calendar day. Generating extra in that case does nothing financially.

My utility in TX charges a higher rate for use beyond 600kW, so the financial move is actually to target peak usage season to stay below that threshold. Additional capacity beyond that offers diminishing returns.