The side quests not only expand your gameplay, but make the main story easier by giving you great equipment and bonus points to level up your characters. They are definately a good thing to fall back on if you cannot beat the main story. Not to mention gold and exp by killing enemies.
Viewing post in Falnarion Tactics jam comments
Earlier on, the chapters prevent perma death for the main characters.
The side characters whom you get from quests or the main story-line can be killed
during missions and you can revive them with an item. This item is a finite source.
Once the item is gone forever, you will no longer be able to use that unit. Resulting in perma-death.
Some characters can again only get injured in the beginning and if Felm dies, it's an instant game over.
If you want an updated version of this game where it's a bit easier yet still challenging and has more content and stat changes.
I suggest buying the game right now on steam. Please note it's in early access and a work in progress, but I will not be updating the game here on Itch.io anymore. The demo was for the game jam only. Please have a nice day~