Hi Fingerscrossed,

My Name's Richard, I have a lot of experience working in endoscopy and alongside the bowel cancer screening team and can hopefully put your mind at rest.

All samples that are removed from the body are sent for testing - This is important to determine exactly what the cells in your polyp are doing. 
As for requesting you to return for another procedure - this would be because of the size, number and type of polyps that were removed. certain polyps are more likely to turn in to cancers (which normally takes years) and if people have those sorts of polyps, we like to check up on them more often. You may well find after your next procedure, you are discharged - again depending on whether or not you have any polyps.

Best Wishes