Thank you for the link to the S4 MK3. Since you can connect the microphone directly to the S4 MK3, you don't really need a (T4S) mixer.
is it just nice to have or highly recommend?
The T4S would still be nice to have and recommended if you are doing Karaoke. The T4S has ToneMatch Presets, zEQ, ParaEQ, Comp/Gate, and effects and reverb that can get great sound for a singer.
The T4S also has ToneMatch Presets for DJ work, and a Master EQ that can help you to get optimal sound for environment at the show.
If you are just DJing, I see no real reason to get a t4 or any outboard mixer.
The l1 usually needs some tweaking of the highs and mids and a typical 3-band eq is usually all I need to shape the sound in almost any setting.
i use a Denon MC6000 mk2. The outputs are plenty hot and the 3-band does the trick.
the DJ mic on controllers tends to suck but if you’re just doing announcements- no big deal.
However, using a T4S makes setup very simple. There are settings for Flat, loud DJ playback, and soft DJ playback that help transitions without flipping the B2 switches.