LA doesn’t come into play; RHD is murkier
ECL matters only for encounter balancing, WBL, and XP. DMs are instructed to consider you based on your ECL when determining appropriate CR for encounters, when determining how much XP you get from the encounter, and how much XP you need to level-up again. When considering your “wealth by level,” ECL is the level in ...
From the DMG p. 172.
Starting Level of a Monster PC: The table above gives the
level adjustment for several monsters. Add a monster’s level
adjustment to its Hit Dice and class levels to get the creature’s
effective character level, or ECL. Effectively, monsters with a level
adjustment become multiclass characters when they take class
levels. Characters ...