*read last part for TLDR*

Think of lightning channels like toll roads you built; if you set the fees to zero, then anyone and everyone will make an use to use your road for free.

If your fees are really high, then very few, if anyone will use the road. Less wear & tear for you to manage

Same for lightning.

If you set fees too low, you may find that you have "spent" (from someone routing through your node) your entire channel balance (all liquidity would be on the other side of the channel)

- this is bad for you because maybe one random day, you decide to make a lightning payment from your node. Guess what? Can't do it! You have zero liquidity to do so, because someone routed all your liquidity without you realizing it. And since fees were so low (or zero) you earned zero sats to cover a rebalancing fee (couple hundred sats+ easy). So it'd cost you to constantly rebalance your channels because you have zero fees

Opposite is true if you have extremely high fees

- this is good for you personally, because most likely you'll have the liquidity where you want it, when you want to make a payment or receive. You'll get less "routing" since it costs more than average, but this is OK because you want to make sure IF someone does route through your node, your rebalancing fees are covered by the fees you collect his routing.

*TBH none of this matters because you'll never be a routing node if you're running via Tor & have less than 1 BTC on there with minimum 10M+ sat channel sizes. Don't overthink it, just use default fees.

This is an art not a science.