Sarcoplasmic muscular hypertrophy involves an increase in the sarcoplasmic volume of a muscle cell with no corresponding increase in muscular strength. A strength increase is something you normally expect with an increase in muscular hypertophy, however sarcoplasmic volume increases serve very little to no functional purpose in terms of strength development.
Sarcoplasmic hypertrophy is a response to hard training at relatively high volumes. In order for muscles to increase in size as a result of an increase in sarcoplasmic volume, they have to be trained within a higher repetition range. This is generally in the range of 8-12 and even beyond. This causes sufficient micro-trauma for the muscle to respond.
Endurance athletes also experience a small level of sarcoplasmic hypertrophy in response to extremely high volumes of training.
Obviously this form of muscular hypertrophy is not desirable for anyone aiming to increase strength or sports performance. Bodybuilders and those wanting beach muscles are likely the only ones concerned with sarcoplasmic muscular hypertrophy. This form or muscle size increase is the main reason you see strength to weight ratio decrease as a person gets larger, even with no evidence of excess body fat. It can seem a mystery to some as to why bodybuilders and frequent gym goers seem to be huge but only moderately strong.
Myofibrillar muscular hypertrophy is what most people want. This is an increase in the size of the actual contractile proteins, resulting in more available muscle for contraction applied to resistance. This form of muscle increase is commonly seen in athletes that perform dynamic sports or strength and power. Weightlifters experience myofibrillar hypertrophy as a result of their training. When a load is lifted that is beyond 75% of maximum a corresponding increase in contractile proteins occurs in order to adapt and lift a heavier load next time.
Myofibrillar muscular hypertrophy is attained through high intensity, lower volume training. However this is not always the case, it is just ideal. A muscle will not increase in strength to any great amount through repetitive lifting until fatigue. It doesn't make sense that lifting something 12 times will increase the amount you are able to lift in one-off efforts that are close to maximum strength. This is why myofibrillar hypertrophy occurs most notably as a result of training in the range of 3-7 repetitions. It's not ideal for a bodybuilder but it will build actual functional strength you can use and not unnecessary bodyweight. The size of the muscle will increase at a slower rate because the hypertrophy involves growth of functional units of muscular tissue as opposed to simply volume.