Dividing string sections into several parts is a common technique called “divisi” and for section strings is usually the preferred way over making the players play awkward double stops. However samples make many composers believe that a divisi will simply give you more notes at the same time without any other consequences. However there are a few things that need to be considered when dividing the sections:
1. The higher you go with violins the more instruments you need to maintain the substance of sound as they start to sound thinner the higher you go. That’s why it usually is better to split up the first violins as last resort if you want them to mantain size.
2. The substance of a divisi sound is of course depending on the size of your string sections but also largely on dynamics. Soft dynamics will often work with lots of divisi, even into more than two parts per section but the louder you get, the more substance you need on the individual lines. So make your choice of divisi depending on your dynamic level.
3. Even though logic might say otherwise the first choice of dividing one section often are the celli. Even if they are lower in numbers than the higher sections, they will usually not have a problem with substance if you divide them into two parts.
4. A special form of divisi is to divide practically all sections in two parts but have the lower part of one section play the same part as the higher part of the next lower section. By that you get even a more homogenous sound out of the strings.
5. Another special form of divisi is to octave divisi sections. The reinforcing harmonics of the lower octave plus the richness in tone colour will create an organ like effect (Aase’s Death from Grieg being one of the most famous examples of that technique with all sections apart of basses divided into octaves, the effect gets most effective around 1:20). Still you need to be prepared to lose substance in the individual voices in that technique.