There ARE exceptions to this basic rule. It all depends on the items each client has. You'll notice some clients' items, especially consistent clients (your weeklies and biweeklies), can be sorted to increase your efficiency and decrease the overall number of loads or time spent per client. The goal is to give each client's items as much care as possible without wasting time or energy.
Use your Judgment
In general, you want to stay true to form as much as possible, keeping in mind, as I have stated before, read the tags whenever you're unsure. For example, you'll note that not all whites can be washed with chlorine bleach.
If a client has a large amount to wash, it is better to take it a step further to prevent dye transfer. For example: sort a load of just red. You would only do this if there was enough red to make a load.
How to avoid unnecessary loads:
Other provider tips have been to use the color catcher product. You could use this to reduce the amount of loads for client's with a single bag by tossing a color catch sheet into a mixed load. Be sure to wash any mixed load on COLD.
Do your best to keep consistent load sizes when possible. You want to have normal to large load sizes to maximize your washing. Work smart! You don’t want to sort into six loads for every regular size bag or you will never finish. Sort into the four categories and then reduce down if possible.