You don't have to sit on the objective, can be very situational as some objectives you can and others you have to find better positioning, at least it has been my experience that enemies always find a way to hit the frontlines rear or hit the objectives that are undefended and recon has to cut that down before it happens so positioning is key for us otherwise we won't be as effective as we should.
Weather you sit on a single position or are constantly on the move it will depend on your strengths as a player. Some are insanely accurate, better at flanking (sneaky), or just spotting it will depends on the player to make their strengths work for the team based on their circumstances (map layout, line of sight, so on....) this is very time consuming so it takes time to figure this out, improve upon, and find counter measures if you find yourself on the opposite side. Personally i enjoy this process
I have to admit I have respect for players that can get to spots that are not meant to be open. I won't deny it pisses me off at times but I can respect their ability to do so, I wish they didn't share how to do it but I like their out of the box thinking and their ability to surprise me. Not saying developers shouldn't fix these issues but I enjoy the unexpected aspect they bring