Is there any impact if we do not use _satellite.pageBottom() on pages with DTM implementation ? We are asked to use it, but even if we don't , the server calls are coming fine, even for rules defined on page bottom or direct call rule script called after _satellite.pageBottom().
If_satellite.pageBottom() is not on the page, normal page bottom processing happens at DOM Ready.
The benefit of an explicit _satellite.pageBottom() is, as I understand it, just one of more precise timing of rule execution. I'd say, just be aware that not everything that is documented to work when called on a page bottom rule will be guaranteed to work later in the window load lifecycle.
You should probably stay away from using page bottom rules in DTM and use DOM Ready instead. This would actually set you up pretty nicely for an eventual move to an asynchronous implementation of Adobe Launch (since there is no _satellite.pageBottom() call in that configuration).