Does urine retention usually cause many symptoms?

Yes. Retention can be partial or complete. Obviously if one cannot void at all the bladder can only stretch so far until it becomes very painful. When someone can empty partially but leave more than 100 cc behind, then frequency of voids increases along with the risk of uti. The cause should be found- most older women have a fallen bladder, and younger ones can have spasms in the pelvic floor muscles.
Agree with Dr C.M. It can also cause overflow incontinence where leakage occurs because the bladder is always full. Overtime the bladder can dilate further and become non functional or even rupture.
Not always. Sometimes it leads to symptoms of frequency, urgency, pressure or frequent infections. In severe cases, it can lead to kidney failure, with absolutely no symptoms.
Here are some ... The variety & degree of u-symptoms from urinary retention vary widely chiefly depending on its pace of development; the faster, the more, and the worse. Its development is a process of lifelong making and displays its Sx along its course of full spectrum. Besides, if its related side effect such as bacterial UTI kicks in, its related symptoms would be serious and even fulminating...