Lets look at some of the advantages and disadvantages. Compared to an IDE system SCSI can cost hundreds of dollars more. Notice that the tasks get divided. As the C drive is being read, D is put on hold. Therefore, If you do a lot of multitasking and time is a factor then a SCSI system is invaluable.
Speed is always an issue no matter what the computing situation is.
Let's look at some numbers. Newer enhanced IDE drives have access rates as low as 9 milliseconds and burst transfer rates of 25 Megs per second. Some of the faster SCSI drives have access rates of 8 milliseconds and transfer rates depend on the SCSI card. An average SCSI 2 card will do a burst transfer rate of up to 25 Megs per second. To conclude, Multitasking is the key to SCSI's value.