Remember that crystals will precipitate with cooling so sediment examined in the laboratory will always show a higher crystal count than the urine as it emerges from the urethra. Crystals also precipitate as pH changes. Proteus infection or contamination of urine can precipitate struvite crystals in a spectacular manner. If it is an infection, treat that first before prescribing diets. Bacterial culture can be done on a free flow sample if you accept that the results may reflect the contamination.
Mixed infections are also more likely to be contaminants.
However if there is dysuria present, the natural defences of the urinary tract are de facto impaired, so it can be useful to know what is around and what it is likely to be responsive to. In chronic or recurrent infections however it is very useful to be able to culture from a cystocentesis sample. Bacterial cultures may be affected by the presence of antibacterials. It is better to sample first and treat afterwards but to be pragmatic leave as much time as possible between the last antibiotic and the sample. With urine, you might succeed in growing something 48 hours after an injection of a short acting antibacterial but you might have to wait 7 days after a course of treatment.