If you already have a low SWR, you don't need the tuner. Normal tune up is to use the Tune to dip the plate and the Load to start bringing the plate current up. keep dipping and bringing the Ip up until you have a very shallow dip left. Some amps you do the same thing but you just peak both controls to get the specified output current or power.
I have a Viking II, which can tune a wide variety of loads, and an Icom-718, which, on the other hand, likes to see pretty 50 ohms all the time. If I only used the Viking II (which, when I first went on the air, was my only TX) I didn't really need a tuner. (Note -- I am fairly new to ham radio, but not to radio. I have been in broadcasting over 50 years, and most of it in engineering and a lot of it in AM stations. So, I started out wanting to be on AM on 160 or 80 meters, and landed on 80 most of the time.) I was able to run my Viking II, into a random wire antenna, comfortably on 160, 80, 40, and 20 without a tuner. BUT....when I added the tuner, I found it easier to always tweak the Viking into the dummy when changing bands, and then match with the tuner. Once I added the Icom, that was the ONLY method that worked. So... do you NEED the tuner ? In the scenario you describe, possibly not. But, I think, based on my experience, the tuner will make life easier.
Most manufacturers instruct users not to operate into SWR's greater than 2:1. The owner's manual for myKWM-2, which has a Pi-Network output warns that damage can result by operating with SWR above 2:1. Antenna and co-ax feed line efficiency start to suffer with high SWR and an antenna tuner doesn't change that. I view antenna tuners like audio output transformers in Hi-fi gear that transforms a high impedance tube circuit 3-5000 ohms to a useable 4, 8, or 16 ohm output. Of course, one doesn't have to contend with feed line losses, just speaker inefficiency.
Balance lines are essentially lossless but require a balun to avoid radiating. Coax likes to see a balun on balanced systems too to prevent radiation and improve efficiency. I try to go for the best match I can then use a tuner if my SWR goes above 3 or 4:1. Tuners add another element of complexity to the system and that is always good to avoid.