As someone who doesn't play LoL much, what are the advantages/reasons behind lane swapping?

you are switching lane opponents with another team mate in hopes that you or him performs better

Assuming you're talking about 1v2, then from my limited understanding: Advantages:

• Reliable farm for your ADC - since even if the jungler comes it'll be a 2v2 with the enemy top laner being low, which necessitates the enemy mid come up to help.

• Avoid bad matchups - If you have a really bad lane matchup against the enemy team you can simply swap and avoid it.

• Skip laning for your top-laner - If your toplaner was picked as someone who has good sustain, good utility, but a bad laning phase, your lane swap is hurting them less then it hurts the opponent.

Disadvantages:

• Lose map pressure and objectives on the side you swapped away from - basically dragon.

• Difficult to deal with midlane roam - since your jungler is probably going to be spending a lot of time helping the swap-ee, that frees up the midlane to roam and make picks, or push and win lane. If you plan to 1v2 from champ select, you should probably pick a lane bully mid.