hi captjns- what aircraft type are you talking about ? and when you say you track a radial outboand - that would be vor navigation, not lnav i think.
in general lnav is very nice being enroute since you do not have to care about things like wind changes and drifts. at approach - like written above- its of course pretty useless when being vectored , and thats mostly the case. on less dense airports you also often get the instruction " descend xxx feet, position yourself 10 miles final rw xx , report when established" . in other words- the atc controller is to lazy to vector you and the airspace around you is free.
on high density airports- frankfurt main e.g you can expect vectors, flying a STAR followed by the published standard ILS is more than rare , it would also take up to much time. and expect questions like " whats your minimum clean speed" ?- reduce as far as possible or keep high speed as long as possible when on approach.
similar at departure - you get a sid with your ifr clearance at startup, but you fly the sid mostly only partially. when clear of altitudes which may conflict with approaching traffic , they handle you over to enroute radar atc which will give you ( in most cases) a direct to an enroute fix and here we go- the sid is for you and atc history. so when cleared via atc to a higher altitude than published for departure its on dense airports a good idea to keep a good climb rate - you will be handled over more quickly .
enroute its sometimes nice to switch in hdg when there is a major course difference between two fixes on your route . leaving lnav engaged would result the ap flies exactly overhead the fix and then goes into a full 25 deg bank - doing it by hdg you can start the turn some seconds earlier and turning the knob slowly smoothens it out . on new track hit "direct to" ( the next fix) and kick in lnav again. the offset to the new fix doing this is that minimal that nobody says a word.
cheers !