Without co2 back pressure you'll end up with dribble pours and flat beer.
Download a psi vs temp for volumes of co2 you want in your beer and adjust your beer line length and size accordingly.
So example, if you serve your beer at 36F and want your beer carbonated to 2.5 volumes of co2, you would want to maintain a keg psi of 10-11psi. This is static and shouldnt change for the whole keg dispensing.
You also want a good consistent pour from your tap, like filling a pint in 6-8 seconds. To do this you need to adjust the total length of your beer line...shorter the beer line, less restriction and a faster pour. Longer means more restriction and a slower pour.
Most beer line runs of under 8ish feet would typically use 3/16" beer line. Start with 8 feet and check your pour. If its too slow, cut a foot off and try again until you get the pour you want while maintaining the 10-11 psi in your keg.
If you make a wide range of beer and want every keg to pour nice and have the proper volumes of co2 in it, you'll need several beer lines. A shorter one for stout for instance, and a long one for wheat beers..