First of all, I will state I am pro forced personal loot. But I honestly find it hard to see a good thing about not having forced personal loot. What is it that makes ML so important in guild runs? I, myself have been in a guild that did cutting edge achievements, and still prefer PL over ML. What I the idea was for ML was to give the items to people that needed it the most, making the people who makes the least effort get the most items from the raids(not grinding m+ for example). All this sounds good, since you literally gear the raid for the greater good, instead of feeding one person. But it feels pretty demotivating to give items to all the lazy people who don't farm gear besides raids.
I mean, that lazy raiders will still get a extra loot even with PL, but instead of getting that wf/tf item you need to upgrade your gear, you get to keep it. It might not even be tradeable because it's a so big ilvl upgrade.
Oh well, enough of why I prefer PL over ML in normal guild groups.
Every new raid tier top guilds race to be the first to down the last boss in the current tier. With every expansion the top 10 guilds play more and more and go to further and further extremes just to get an edge over the others. Split raids is a great example of what happens just to get an edge gearwise to clear everything before anyone else. Guilds makes 5 split farm groups and funnel all the gear to the main raiders with ML. This gives them a huge edge compared to any top 50 guild that dont have time for 5 split farm groups AND progression afterwards. I believe this will be way more balanced in BFA due to personal loot. Simply because undergeared alts can't give all the good pieces to main raiders without having the same ilvl item themselves.
This makes it WAY harder to split farm, making the top 10 guilds more equal and a better "race" to world first (IMO).