Real Musicians and Rhythmic Complexity
One of the most common reasons for slowdowns in recording sessions with real musicians are (unnecessarily) tricky rhythms. As a composer/orchestrator you should always be sure that real musicians are not sequencers that can play all sorts of tricky rhythms easily. But also seemingly simple rhythms that are notated badly can cause major problems.
As soon as your rhythmical subdivision in a quarter note based time signature gets to 16ths or even smaller note values, you should become particularly careful with notations. Avoid 16th rests where possible and generally try to find the easiest readable way of notating things.
Even more problematic are odd meters that come with an inherent subdivision, E.g. 7/8 subdivided into 4+3 or the other way around. Remember that the conductor will not conduct 8th notes but the subdivisions. If the rhythm you notate accents against this subdivision, you’re most likely in for trouble and should try if you really need this counter rhythm and then see if you can notate it in any way that it is understandable. This might even take some time to try out a few different ways of notating things.
For scoring sessions you should always go for the easiest readable even though it might be not exactly what has been intended regarding the individual note lengths (e.g. if it’s easier readable to notate an eighth note with a staccato dot than a single 16th note, go for the eighth, even though there might be a different interpretation of how long this note should be).