I agree that the major purposes of late round picks are for deal sweeteners and to be flipped for picks one round earlier in the following years draft.
Having said that , I think there are three other important aspects of late round picks.
1. This is where you often find your specialists. Kickers, punters, returners of kicks and punts, long snappers etc.
2. This is where you take flyers on Div 2 and Div 3 stars who may be diamonds in the rough
3. This is where you draft higher ranked players who fell due to injury or character concerns. No, Tua won't be available in round 5, He may not be available at pick 5 but a 3rd round rated player may be available in round 5. With medical rechecks being an issue because of COVID 19, we may just get lucky in round 5 this year.