expensive but hellishly fast

An SSD is not simply a replacement hard drive but a real upgrade, where you can measure the performance of other system components. Even if the storage media is crammed to a large extent, reduces the new system starting time in an imperceptible context. In a few seconds the freshly booted computer is fully operational.
In addition, the only thing that still emits a noise of the fan.
Since there are no moving parts, the media is fall proof and the power consumption is low and thus the battery life of the laptop noticeably longer.
Only the price per GB is high but, in terms of added value, perfectly adequate.